Drill and Tap Selection: Getting the Details Right on Every MRO Job
Nobody thinks much about drills and taps until a stripped thread stops a machine rebuild cold. In the MRO world, cutting tools are a cost line item that usually gets bought on price and habit — which is exactly why they cause so many avoidable problems. Selecting the right drill point, tap style, and material for the job is not glamorous, but it is where real savings live.
Point Geometry Matters More Than You Think
A 135-degree split point starts on contact and reduces walking — essential for CNC and portable drilling in hardened or angled surfaces. A 118-degree conventional point is fine for general-purpose drilling in softer materials. Using the wrong point geometry is the #1 cause of oversized, off-location holes in maintenance work.
Black Oxide vs. Black & Gold: Black oxide drill bits get their coating from a conversion process that improves lubricity and corrosion resistance — the standard for general MRO drilling. Black & Gold (bright finish with gold oxide treatment) is a stepped-up option for applications where chip flow and heat resistance matter. Both are HSS with a 135-degree split point in the jobber-length range.
Taps: Match the Tap to the Thread You Actually Need
- HSS hand taps are the general-purpose default for through and blind holes in most materials.
- Spiral point (gun) taps push chips ahead of the tap — ideal for through holes in softer materials.
- Spiral flute taps pull chips out — the right call for blind holes.
- NPT pipe taps (carbon or HSS) cut the tapered threads required for pipe fittings — a different animal entirely from machine screw threads.
- Combo drill & tap sets save a full operation when you need a drilled and tapped hole in one pass.
For stainless and high-temperature alloys, step up to cobalt. Cobalt HSS holds its edge at the elevated temperatures that kill plain HSS, which makes it the default for repair work on process equipment where you cannot always identify the alloy before you drill it.
Reamers: The Precision Finishing Step
Bridge and car reamers deliver the accuracy that a drill alone cannot. If a rebuild calls for a press-fit or a critical dowel hole, drill undersized and finish with the correct reamer. It is an extra step that prevents an oversized hole you cannot un-drill.
The Takeaway
Stock your toolbox with the right points, the right coatings, and the right tap styles — and match them to the material before you start. A USD 5 difference in tool cost is nothing compared to a USD 500 mistake in scrap or a USD 5,000 hour of downtime.
Related catalog item: RBC Industrial carries the full BBI Proferred cutting tool line — HSS jobber and mechanics length drills, cobalt drills, combo drill & tap sets, spiral point gun taps, HSS and NPT pipe taps, bridge and car reamers, step drills, and TCT hole cutters — available for same-week delivery across the El Paso region.
Need help building a maintenance drill-and-tap kit that actually covers your equipment? Call (915) 845-8188 or visit www.rbc-industrial.com.