Drilling 3/8" hole in an Arca-Swiss rail base?

**David Lindquist** · 23-Nov-2011, 20:31

Originally Posted by Leigh

The standard tripod thread in that size is 3/8"-16, the '-16' meaning 15 threads per inch.

If you want to actually cut the treads in the rail, you drill a 5/16" hole, then use a T-handle to drive the 3/8-16 tap into the hole, thus cutting the threads.

Unless you have a proper drill press and a vise or similar device to hold the rail in position while it's being drilled, I would suggest having it done by a professional machinist or shop teacher. It's a five minute job for someone with the right tools.

- Leigh

Hi Leigh, Is it too late for you to edit this to "... -the '16' meaning 16 threads per inch."

I always appreciate your skilled and informative posts here and on PM.
David

**Leigh** · 23-Nov-2011, 21:57

Hi David,

Yeah, typo. That's what I get for not proof-reading the post, as I usually do.

Thanks,

- Leigh

**winterclock** · 24-Nov-2011, 03:17

From your description it is definitely a PEM nut, it gives the tripod screw some meat to hold onto. If the thickness of the rail metal is only about 1/8" that will not be enough threaded thickness for the screw. The PEM nut has ridges that when pressed or pulled into the aluminum of the rail, actually form grooves to hold it in place and keep it from spinning. They require a carefully sized hole which is why I recommend someone with a vertical mill cuts the hole. It will need to be pulled into place if you only want one hole in the rail. This can be done with a bolt, nut, and a couple of washers

**Steve Smith** · 24-Nov-2011, 03:31

Something else to consider if this is a heavy camera. See if you can find out what thread the screw in the tripod is. It could be British Standard Whitworth or UNC.

Steve.

**John Koehrer** · 24-Nov-2011, 13:49

There are inserts available from Menards and others(Pem nuts?)
inserted with something that looks like a POP rivet tool but the arbor rotates and squeezes the nut onto the metal the nut is inserted to.

I'd agree that 1/8" isn't enough to tap without risk of the insert just pulling out and damaging the rail.

Regarding Steve's comment re the technical size of the screw, I've never had a problem with the local Hdw Store having the inserts or T-nuts. They're likely to be UNC though.

**Steve Smith** · 24-Nov-2011, 15:19

Originally Posted by John Koehrer

Regarding Steve's comment re the technical size of the screw, I've never had a problem with the local Hdw Store having the inserts or T-nuts. They're likely to be UNC though.

Traditionally, tripod threads were 1/4" and 3/8" Whitworth but now they are just as likely to be UNC. There is a five degree difference in the cutting angle of these threads so with a tripod screw with one thread in a camera with the other, the faces of the threads will not be in contact over the whole area. With a light camera it probably won't make much difference but with a heavy camera, matching threads will give a more secure fitting.

Steve.

**r.e.** · 24-Nov-2011, 16:36

Thanks for all the input. Very helpful.

**Jeffrey Sipress** · 24-Nov-2011, 19:17

Probably not a Pemnut, but rather a Keensert. Not really necessary unless you plan to thread something into it repeatedly. To create a tapped hole in your rail, just find a local machine shop. Forget about the high school! Get it done right.