Advertising Disclosure
Our rankings are cleverly generated from the algorithmic analysis of thousands of customer reviews about products, brands, merchant’s customer service levels, popularity trends, and more. The rankings reflect our opinion and should be a good starting point for shopping. By purchasing the products we rank, you’ll get the lowest price we found while we may receive a commission at no cost to you, which will help us continue to provide you with value.
Best Choice Meccion 
Meccion Wood Drill Bit 25mm x 165mm Professional Self Feed Speed Auger Drill Bit 1/4 Inch Hex Shank Woodworking Hole Dri Premium Wood Drill Bit - Made of High Carbon Steel with a cutter hardness of at least 50 HRC, Reliable performance for wDEWALT 
Dewalt Self-Feed Forstner Wood Drill Bit, 25 mm Size Special drill bit made with a high percentage of carbon steel
1-12x Auger Wood Drill Bits Fast Cut Spade Bits Holesaw Self-feed Boring 10-35mm 12Pcs SPEED Fast Cut Spade Bits Auger Wood Drill Bits Holesaw Joiner Carpenter Self-feed Boring 10mm to 35mm. 1-14x 6-35DEWALT 
Dewalt Self-Feed Forstner Wood Drill Bit, 54 mm Size Special drill bit made with a high percentage of carbon steel
ZAMIN High Carbon Steel Self Feeding Feed Drill Bit Wood Auger Drill bit 25-76mm Zamin Self feed bits made from "milwaukee" OEM Factory. For selffeed bits, auger bits and hole saw 1 in. shank Extend yoBosch 
Bosch SF2001 2 In. Self-Feed Drill Bit 7/16 In. hex shank for reduced slippage (3 In. and larger three-flat shank)Best Value Bosch 
Bosch CC2430 Clic-Change 3-Piece No. 6, No. 8, and No. 10 Self-Centering Bit Assortment CONVENIENCE: Change Bits Without Re-ChuckingTools Self-Feed Drill Bit – 2-Cutter Self Feed Drill 3-inch – Professional Bo... Professional self-feed drill by Sabre Tools;. Our wood drill bits feature an aggressive feed screw thread and sharp, deeDewalt Dewalt Self-Feed Wood Forstner Drill Bit, 76 mm Size, Silver/Black Special drill bit made with a high percentage of carbon steelMilwaukee 2" Self feed Bit/Hole Hog/Drill Bit/ 10X Faster New #48-25-2002 Be sure to check out all of our other drill bits, tile bits, plumber's bits, electricians bits, hand tools, hats, clothiYakamoz Yakamoz Self Centering Drill Bit, 4PCS HSS Door Self-Centering Hinge Hole Opening Drill Bit Set丨5/64, 7/64", 9/64", 11/6 High speed steel with a brass body designed, durable and excellent for useIRWIN Irwin 3041004 Speedbor Max 3/4-Inch by 6-Inch Self Feeding Spade Bit A fast speedbor spade bit that features a Tri-Flute design with a fast chip ejection12Pcs SPEED Fast Cut Spade Bits Auger Wood Drill Bits Carpenter Self-feed Boring 12Pcs SPEED Fast Cut Spade Bits Auger Wood Drill Bits Holesaw Joiner Carpenter Self-feed Boring 10mm to 35mm. 12Pcs SPEEIrwin Tools Irwin 3041002 Speedbor Max 5/8-Inch by 6-Inch Self Feeding Spade Bit A fast speedbor spade bit that features a Tri-Flute design with a fast chip ejectionLot of 5 Milwaukee Self Feed Drill Bits & 1 Lenox Self Feed Drill Bits Plumber 5 Milwaukee and 1 Lenox. See list below. This is a lot of 6 Self Feed Plumbers Bits. These are in good Pre-owned conditi17% Off Bosch Professional Bosch Accessories Blue 19-Piece PointTeQ HSS Twist Drill Bit Set (For Metal, ProBox, Ø 1.0–10.0 mm, Drill Driver Accesso Saves time: The HSS Twist Drill Bit PointTeQ with reduced shank enables you to drill through metal quickly thanks to theMilwaukee 49-22-0030 Plumber Self Feed Drill Bit Set 3 Drill Bits 49.99The Milwaukee 49-22-0030 Plumber Self Feed Drill Bit Set includes 3 drill bits designed for professionals in the plCentury Drill & Tool Century Drill & Tool 38304 Self Feed Wood Drill Bit Replacement Screw Designed to work for all wood projects especially suited for furniture making cabinetry and doweling where an exact holeIRWIN 2-9/16" & 2-1/4” WeldTec Self-feed Drill Bits Irwin self-feeding wood bits.Bosch Professional Bosch Professional HSS Twist Drill Bit PointTeQ ToughBox Set (for Ferrous Metals, Ø 1 - 10 mm, CYL Shank, Self-Centering Content: 18 piecesDeWalt Joiners Tool 35 mm Self Feed Drill Bit Wood Timber Dewalt 35 mm Self Feed Drill Bit. Aggressive spur provides fast material penetraion. 7/16" Ball groove shank for quick cBosch Bosch Accessories Professional 5-Piece HSS-G Metal Drill Bit Set (for Ferrous Metals, Non Ferrous Metals, Ø 2-6 mm, 1/4" HSS Twist Drill Bit offers high precision drilling for standard usage with metalSUTTON TOOLS 3pce SELF-FEED SPEEDBOR STYLE 4 -FLUTE WOOD AUGER DRILL BIT SET Sutton Tools Four Flute Auger Bits are designed for machine and hand drilling into hard and soft wood. Sutton Part No. EFavson 2pcs 10mm Wood Drill Bits, Auger High-Carbon Steel Fast Cut, Professional Self Feed Speed Drill Set, 1/4 inch Hex Shank Premium Materials: Wood drill bits are made from high quality 45# carbon steel for durable.Milwaukee 49-22-0030 Plumber Self Feed Drill Bit Set 3 Drill Bits This is a NEW - unused Milwaukee 49-22-0030 Plumber Self Feed Drill Bit Set 3 Drill Bits. Plumber Self Feed Drill Bit SeGreycore Greycore Tools Self-Feed Drill Bit – 2-Cutter Self Feed Drill 3-inch – Professional Boring Drill Bits for Woodworking – Designed for Professionals: The Greycore Tools wood boring drill bit is specially engineered to improve wood drilling peFreud-Diablo DB SELF Feed BIT 2-1/8 in, Multicolor, DSF2125 Freud DSF2125 Features Feed Screw with Pull Out Stop design prevents the feed screw from slipping out when the bit is reDewalt Dewalt Self-Feed Forstner Wood Drill Bit, 68 mm Size Special drill bit made with a high percentage of carbon steel2 MIBRO INDUSTRIAL 1-3/4" SELF FEED MULTI SPUR WOOD BORING DRILL BITS 458531 Model Number: 458531. The Removable Coarse Threaded Screw Quickly Pulls The Bit Through The Work Leaving A Smooth Hole EIRWIN Irwin Industrial Tools 3046009 1-3/4-Inch 3-Cutter Self Feed Drill Bit 1-3/4" Diameter Speed or Max Self Feed Wood Drill BitMilwaukee 48255150 Switchblade -Self Feed Drill Bit 2& 9/16 NEW (48-25-5150) 2 and 9/16 Milwaukee self feed drill bit new Be sure to check out our other tools to accessories drill bits, electricianDiablo Diablo by Freud DSP2930-S9 9 pc SPEEDemon™ Spade Bit Set (9-Piece) 9-Piece Set - Includes a versatile range of spade bits from 1/4", 3/8", 1/2", 9/16", 5/8", 11/16", 3/4", 7/8" and 1". IdCrescent CDSF-577 Self Feed Drill Bit | 5 In x 3 In | The Crescent Self Feed Bit features resharpenable blades that are long lasting for continuous optimal cutting. The centeMilwaukee Milwaukee Speed Feed Wood Drill Bit (3-Piece Set) Double wing spurs for drilling fast holes in woodWakects 8pcs Twist Drill Bit Set, 200mm Extra Long Spiral Drill Bit High-Speed Steel Straight Shank Twist Drill Bits Set Tool 4- These twist drill bits are made of high-speed steel for high hardness and durability, sturdy andDEWALT Dewalt Self-Feed Forstner Wood Drill Bit, 117 mm Size Special drill bit made with a high percentage of carbon steelBosch Bosch Accessories Professional 5-Piece HSS-G Metal Drill Bit Set (for Ferrous Metals, Non Ferrous Metals, Ø 2-6 mm, 1/4" HSS Twist Drill Bit offers high precision drilling for standard usage with metalMilwaukee Milwaukee 48255125 SwitchBlade 38mm Selfeed Bit Aggressive feed screw design allows the bit to pull through the wood faster, resulting in faster drillingMilwaukee Milwaukee Speed Feed Wood Drill Bit (3-Piece Set) Double wing spurs for drilling fast holes in woodIRWIN Irwin Industrial Tools 3046013 2-9/16-Inch 3-Cutter Self Feed Drill Bit This are easy to useDiablo Diablo by Freud DSP2930-S9 9 pc SPEEDemon™ Spade Bit Set (9-Piece) 9-Piece Set - Includes a versatile range of spade bits from 1/4", 3/8", 1/2", 9/16", 5/8", 11/16", 3/4", 7/8" and 1". IdBosch Bosch SF5018 3 piece Self-Feed Bit Replacement Kit 7/16 In. hex shank for reduced slippage (3 In. and larger three-flat shank)IRWIN Irwin Industrial Tools 3046006 1-1/4-Inch 3-Cutter Self Feed Drill Bit This are easy to useCrescent Crescent Self Feed Drill Bit | 3-5/8" x 5" | CDSF-583 Long lasting blades that can be resharpened for optimal cuttingCentury Drill & Tool Century Drill and Tool 38334 2-1/8-Inch Self Feed Wood Drill Bit High carbon steel for maximum strength and durabilitySutton Tools Sutton Tools P&N Quickbit Self Centering Hex Shank Drill Bit, 1/8-Inch Thread Diameter 1/4-Inch hex shank suits quick change adaptorsIRWIN Irwin Industrial Tools 3046008 1-1/2-Inch 3-Cutter Self Feed Drill Bit This are easy to useMengshen Mengshen Co Step Drill Bit 4-32mm Spiral Groove, M35 HSS Multi Hole Cutting Enlarge Stainless Steel Plate Quenching Stee Much More hardness - M35 HSS is harder lot than HSS 4241, suit for drilling in stainless steel plate & quenching steel pIRWIN Irwin Industrial Tools 3046007 1-3/8-Inch 3-Cutter Self Feed Drill Bit This are easy to useWakects 8pcs Twist Drill Bit Set, 200mm Extra Long Spiral Drill Bit High-Speed Steel Straight Shank Twist Drill Bits Set Tool 4- These twist drill bits are made of high-speed steel for high hardness and durability, sturdy andCentury Drill & Tool Century Drill & Tool 38306 6" Self Feed Wood Drill Bit Extension Securely grips self feed bits for extended reachBosch Accessories Bosch Accessories Bosch 1pc. HSS-G Drill Bit (Metal, Hard Plastic, Ø 7 x 69 x 109mm, Accessories Drill Driver) suitable for drilling alloyed and non-alloyed steel up to a tensile strength of 900 N/mm²DEWALT DEWALT Drill Bit, Ship Auger, 1 Inch x 6 Inch (DW1671) Fast material penetration with self-feed spurDEWALT DEWALT Drill Bit, Self Feed, 3-5/8 Inch (DW1641) Aggressive spur provides fast material penetrationYakamoz Yakamoz 16 in-1 Center Drill Bit Set, 8pcs 1/4" Hex Shank Self Centering Hinge Hole Drilling Tool Kit for Woodworking Wi High speed steel drill bit and brass body with electroplating; Standard 1/4" hex shank fits all power drill bit and quicSTROTON Metric M42 8% Cobalt Twist Drill Bits Set for Stainless Steel and Hard Metal (1mm-10mm/19pcs) Premium M42 8% Cobalt Steel ,68-70 HRC (Rockwell Hardness Scale) ,Usually Give the Best Heat,Wear and Chip Resistance anIRWIN Irwin Industrial Tools 3046004 1-Inch 3-Cutter Self Feed Bit This are easy to useRIZGHWOY RIZGHWOY Electric Capping Machine Bit Automatic Heading Mat for Automatic Mat Electrico Self Feed Drill Bits To Install: The ensures a and for leak lid, which for seals the bottle in a place after use.Hymnorq Hymnorq Step Drill Bit Set of 3pcs, 4 to 12mm / 20mm / 32mm, HSS with Black Nitride Coated, Self-Centering Split Point, 3PC METRIC SET - The set includes 3 step drill bits(4-32, 4-20, 4-12) which can replace 29 individual drill bits. That mBosch Professional Bosch 7X Expert Self Cut Speed Spade Drill Bit Set (for Softwood, Particleboard, Ø 16-32 mm, Professional Accessory Rota Up to 3x faster than Bosch 2609255269 Spade BitIVY Classic IVY Classic 10765 1-3/4 x 5-inch Heavy-Duty Self-Feed Bit, High-Speed Steel, 1/Card Designed for plumbers and electricians to bore holes in wood to run pipe and conduit, Swift Bore (Registered Trademark)Bosch Accessories Bosch Accessories 7-Piece Masonry Drill Bit Set (Natural Stone, Ø 3/4/5/5.5/6/7/8 mm, Accessories for Impact Drills) Tool holder: cylinder shankIRWIN Irwin Industrial Tools 3046014 3-Inch 2-Cutter Self Feed Drill Bit Country of Origin:ChinaQWORK QWORK Vix Bits Self Centering Clic Change Door Hinge Drill Bit Set High-speed steel, 5/64", 7/64", 9/64", 11/65", 5mm, 1 1) Drill bit size: 5/64", 7/64", 9/64", 11/64", 5mm,13/64", 1/4"Sutton Tools Sutton Tools P&N Quickbit Self Centering Hex Shank Drill Bit, 5/64-Inch Thread Diameter 1/4-Inch hex shank suits quick change adaptorsSpeedbor Speedbor 1877239 Irwin Tools Max Wood Drilling Bits, 4-Inch, 6-Piece Three cutting spurs for faster, cleaner holes, less breakout and extended drilling lifeBosch Accessories Bosch Accessories 7-Piece Masonry Drill Bit Set (Natural Stone, Ø 3/4/5/5.5/6/7/8 mm, Accessories for Impact Drills) Tool holder: cylinder shankSutton Tools Sutton Tools P&N Quickbit Self Centering Hex Shank Drill Bit, 5/64-Inch Thread Diameter 1/4-Inch hex shank suits quick change adaptorsIrwin IRWIN 1869386 WeldTec Self-Feed Wood Drilling Bit, 1 1/2-Inch Innovative welded cutting edge for extreme life in tough materials, including nail-embedded woodVermont American Vermont American 14487-58-Inch Self Feed Stubby Spade Bit, Drill Accessories Black oxide stubby length spade bitsDEWALT DEWALT DW1687 1-Inch by 17-Inch Ship Auger Bit Fast material penetration with self-feed spurIRWIN Irwin IWAX2009 Self-Feed Bit 2-9/16In Speedbor Supreme CHARGE THROUGH NAIL-EMBEDDED WOOD: High-speed steel cutting edge maintains its sharpnessONIGUARD for Milwaukee 48-13-0600 6-1/2" Speed Feed™ Wood Bit Set (6 PC) Self-Feeding Wood Bits are made for drilling fast holes in clean wood. The double wing spurs cut clean holes for feedingLenox Lenox 1787506 Bi-Metal Self-Feed Bit Kit, 16 Piece EXTREME DURABILITY, High speed steel cutting edge for superior durability in nail-embedded woodMilwaukee Wood Drilling Bit, 3In.Dia., Self Feed Manufacturer: MilwaukeeIRWIN Irwin IWAX2009 Self-Feed Bit 2-9/16In Speedbor Supreme CHARGE THROUGH NAIL-EMBEDDED WOOD: High-speed steel cutting edge maintains its sharpnessVermont American Vermont American 14487-58-Inch Self Feed Stubby Spade Bit, Drill Accessories Black oxide stubby length spade bitsLenox Lenox Tools 1787566 Bi-Metal Self Feed Bit, 2-9/16-Inch Extreme Durabilitygreywolf Greywolf Cobalt Drill Bit Set, 19 pcs M35 High Speed Steel Twist Drill Bits, Metal Drill Bits for Hard Metal, Stainles 【Convenient Size Selection】: This 19 pcs M35 drill bit set includes everything you need to meet all your needs, bringingLenox Lenox 1787506 Bi-Metal Self-Feed Bit Kit, 16 Piece EXTREME DURABILITY, High speed steel cutting edge for superior durability in nail-embedded woodYakamoz Yakamoz 20Pcs 0.3-1.6mm Shank Mini Micro Drill Bit Set Twist Drill DIY Kit Rotary Hand Tools 100% Brand New and High Quality HSS Drill Bit.LEDON LEDON 13 PCS Quick Change Hex Shank Drill Bits Set HSS Steel Wood Timber Drilling 13PCS Hex Shank Drill Bit Set 1.5-6.5MMLenox Lenox 1787602 Replacement M6 Screw for Bi-Metal Self-Feed Drill Bits (5-Pack), Small Use this to replace worn screw tips on self-feed hole saw pilot drill bits.Bosch Accessories Bosch Accessories 10-Piece HSS-R Metal Drill Bit Set (for Metal, Titanium, Ø 1-10 mm, Accessories for Drills) Twist drill bits made of high speed steel for drills guided by hand and used in stationary applicationsHORUSDY Horusdy 99-Pieces Titanium Drill Bit Set, HSS 1.5mm - 10mm Size, High Speed Twist Drilling Bits Kit for Metal, Plastic, TITANIUM | HIGH-SPEED STEEL: Classic High-Speed Steel Construction With Titanium Coating For Proven Capability And Durab16% Off ZONADA ZONADA 1/4” Hex Shank HSS Drill Bits, 13pcs in Set Titanium Coated Drill Bits, 1.5mm-6.5mm, High Speed Steel Quick Chang Set of 13 pieces ZONADA Drill Bits. Size 1.5mm(1/16inch), 2mm(5/64inch), 2.5mm(3/32inch), 3mm(7/64inch), 3.2mm(1/8inch),Bosch Professional Bosch Accessories 70 Piece X-Line Drill and Screwdriver Bit Set (for Wood, Masonry, and Metal, Accessories for Drills) For fast, clean drilling in the most diverse metals, Plexiglas and hard plasticsDiablo Diablo 6 pc SPEEDemon Spade Bit Set (6-Piece) 6-Piece Set - This set features # of bits: 3/8", 1/2", 5/8", 3/4", 7/8" and 1".Meichoon Meichoon Forstner Drill Bits 35mm Carbon Woodworking Tool Punching Bit Wood Slabs Flat Wing Drilling Hole Hinge Cemented ★ High Quality - Small incision resistance, improve the opening speed, chip easy and no tremor. The perforation is neat,Bosch Accessories Bosch Accessories 15-Piece Mini-X-Line Mixed Drill Bit Set (Metal, Masonry, Wood, 3x Ø 3/4/5/6/8 mm, Accessories for Dri For use in masonry, limestone, natural stone and artificial stoneBosch Accessories Bosch Accessories 7 Piece Mini-X-Line Wood Drill Bit Set (for Wood, Ø 3-10 mm, Accessories for Drills) Practical borsch mini-x-line box keeps everything neat and tidyAmazon Basics Amazon Basics Drill and Driver Multi-Bit Set - 100-Piece 100-piece drill and driver multi-bit set; ideal for metal, wood, plastic, masonry, and hole sawsVearter Vearter 5PCS HSS M2 Twist Drill Bit Set, 5/6/8/10/12mm Hex Shank Quick Change Jobber Drill Bit, Titanium Coated Metal Dr Package & Size - 5PCS Hex Shank Drill Bit Set comes in a durable plastic case with hanging hole for easy storage and retHymnorq Hymnorq 1/4 Inch Fractional Size M35 Cobalt Steel Twist Drill Bit Set of 10pcs - Jobber Length and Straight Shank - Extr Industrial-Grade M35 Cobalt Steel: Made with 5% cobalt-enriched M35 steel, these 1/4" drill bits deliver superior strengBosch Bosch Accessories Professional 7-Piece Mini X-Line Metal Drill Bit Set (Metal, HSS-G, Cut, Accessories for Drill Drivers Suitable for alloyed and unalloyed steelBosch Professional Bosch 1x Expert Self Cut Speed Spade Drill Bit (for Softwood, Particleboard, Ø 26,00 mm, Professional Accessory Rotary D Up to 3x faster than Bosch 2609255269 Spade Bitgreywolf Greywolf 25 Piece Wood Drill Bit Set, Double Slot Design Wood Drill Bit Set (1mm - 13mm), Durable Box with Index, for Wo 25 pcs woodworking drill set includes sizes: 1*1mm/1*1.5mm/1*2mm/1*2.5mm/1*3mm/1*3.5mm/1*4mm/1*4.5mm/1*5mm/1*5.5mm/1*6mmBosch Professional Bosch Accessories Blue 13-Piece Self-Cut Speed Spade Bit Set (For Wood, 1/4 Inch Hexagonal Shank, Ø 10-32mm, Drill Acces Content: 13 piecesZONADA ZONADA 7pcs in Set 300mm Extra Long Twist Drill Bits, Hardened High Carbon Steel Tools 4-10mm for Wood Hole PVC Plastic - Set of 7 ZONADA Extra Long Drill Bits. Durable & strong, it is made by high quality high carbon steel, and with heat tIrwin Tools Irwin Tools 3046002 Speedbor MAX Self-Feed Wood Bit Extension, 12" Adds 12 inches to SPEEDBOR Max Self-Feed wood drilling bits.DEWALT DeWalt Self-Feed Forstner Bit Set (8 Pieces) Optimized cutting angle delivers longer bit lifeFreud-Diablo DB SELF Feed BIT 2-1/4 in. DB SELF FEED BIT 2-1/4 IN.Freud-Diablo DB SELF Feed BIT 3-5/8 in. DB SELF FEED BIT 3-5/8 IN.Tomvorks High Speed Steel Extra Long Twist Drill Bit Set, Bits for Wood, Aluminum, Plastics, 5 Drill Bits 2mm-5mm, Most Popular S [Extra Long Cutting ] With a length of 150mm~160mm, these drill bits allow for deep hole drilling in various materials.Plmvhpb Plmvhpb 13Pcs Left Handed Drill Bit Set Extractor Drill Bits for Metal Power Tools Accessories with Titanium Nitride Coa Attachable to reversible drills to remove screws, bolts and studs around the house, garage or on the job site.Freud-Diablo DB SELF Feed BIT 3-5/8 in. DB SELF FEED BIT 3-5/8 IN.Diablo DB SELF Feed BIT 2-1/8 in. DB SELF FEED BIT 2-1/8 IN.Bestgle Bestgle 20 Pcs Mini Micro Drill Bits 0.3-1.6mm Shank Twist Drill HSS Small Twist Drill Bit Set DIY Manual Hardworking Ki Different Sizes - 20 pcs small twist drill bits including 0.3mm, 0.35mm, 0.4mm, 0.45mm, 0.5mm, 0.55mm, 0.6mm, 0.65mm, 0.Tomvorks High Speed Steel Extra Long Twist Drill Bit Set, Bits for Wood, Aluminum, Plastics, 5 Drill Bits 2mm-5mm, Most Popular S [Extra Long Cutting ] With a length of 150mm~160mm, these drill bits allow for deep hole drilling in various materials.Meichoon Meichoon Forstner Drill Bits Upgraded Version Multi-Tooth Higher Hardness Carbon Woodworking Tool Punching Bit Wood Slab 【Advanced technology manufacturing and durable material】 Made of Tungsten steel and being hot-treated, the blade is charREED Reed Tool B74 Self-Feed Bit, 4-5/8-Inch Nominal pipe capacity: 4 IPS - 4 CTSIRWIN Irwin Tools 3046003 Speedbor MAX Self-Feed Wood Bits, 18" Drill bits have 3 cutting edges that are hardened for durability and long life in tough materialsMeichoon Meichoon Countersink Drill Bit 4 Pack Hex Shank Depth Adjustable Quick Release 3in1 Wood Pilot Bits Drilling 6# 8# 10# 1 ★ Versatile functionality - The drill is equipped with a 46# steel chamfering device, including an adjustable screw forVearter Vearter 5PCS Twist Drill Bit Set 5/6/8/10/12mm, HSS M2 Jobber Drill Bits with Hex Shank Quick Change, AITiN Coated Metal Package & Size - Drill bits for metal come in a durable plastic case with hanging hole for easy storage and retrieval. SMeichoon Meichoon 3-Cutter Forstner Drill Bits Upgraded Version Higher Hardness Carbon Woodworking Tool Punching Bit Wood Slabs F 【Special Design】 3-cutter Forstner drill bit has faster cutting speed and longer service life. With these sharp drill bi