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This is a single high-speed steel taper tap in the 8-40 thread size, made by Reiff & Nestor, a Pennsylvania company that has been grinding taps since 1912. The 8-40 size has become a go-to among gunsmiths mounting scope bases, and this taper style is the one you reach for to get a hole started right. The gradual lead-in chamfer eases the tap into the material a little at a time, which keeps the threads square with the workpiece and takes a lot of the guesswork out of getting things aligned.
Most factory bolt guns come drilled and tapped for 6-48 base screws, and for plenty of rifles that works fine. The move to 8-40 gives you a larger diameter fastener with more thread contact, which matters on hard-kicking calibers or when you are hanging a heavy scope up top. A common approach is chasing the existing factory holes with a #19 drill and a #8 counterbore, then running the tap to open them up to 8-40. Same story on older receivers where the original screws have rusted or turned out and you want to upsize.
High-speed steel holds its edge and stays hard even as it heats up, so it cuts consistent threads through repeated use. Go slow, use good threading oil or tapping paste, and back the tap out often to clear chips and re-lube. That habit is the difference between a clean hole and a bad afternoon, since a small tap like this does not forgive rushing. On a taper tap the cutting load is spread across more of the chamfer, which is exactly why it is the smart choice for starting a hole.
Use the correct tap drill for the job, keep the tap true to the bore, and this is the kind of tool that pays for itself the first time you set up a rock-solid scope mount.
It is most often used to thread or re-thread scope base holes on rifle receivers to accept the larger 8-40 base screws. The taper style is designed to start the thread, easing into the material with a long chamfer so the threads run square with the workpiece. Many gunsmiths open up factory 6-48 holes to 8-40 for extra strength on heavy scopes or hard-recoiling calibers.
The 8-40 fastener is larger in diameter and gives you more thread contact, which adds holding strength for heavy optics and stout recoil. It also lets you clean up and true holes on receivers where the factory holes were drilled slightly off. If the 6-48 setup is working for your rifle there is no requirement to change, but 8-40 is a solid upgrade when you want the extra insurance.
A #29 drill is the standard tap drill for an 8-40 thread. If you are opening up existing factory holes, a common method is chasing them with a #19 drill and a #8 counterbore to guide everything true. Always confirm your setup is aligned with the bore before you cut.
Small taps break when they get rushed or run dry, so patience is everything. Use plenty of threading oil or tapping paste, turn a quarter turn, then back the tap out to clear chips and re-lubricate before continuing. Keeping the tap square and going slow will get you clean threads every time.
| UPC | 887861082747 |
|---|---|
| Manufacturer | |
| Quantity | 1 |
| Style | Taper |
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