anthonytsi

What tap size is the front brake caliper guide pin bolt on my 94' Grand?
Need to know so that I can drill and tap for a heli coil. It stripped.
Thanks in advance.

anthonytsi

Called around a few places b4 I got some one who knew anything and they told me the tap was 5/16 x 18 coarse thread.
Anyone disagree?

5-90

That sounds about right. However, a very useful tool I've picked up in the last year or so is a "Thread Detective" - got it from MSC Direct for about twenty-five bucks. It's a number of aluminum bungs with an internal and external thread on a cable, they're all marked. Common sizes from #10 to 1/2", and about M5 to M12.

Best thing to do when you're not sure? Measure the damned thing yourself! Then, you know.

anthonytsi

Thanks for that info.
I did measure it myself and the "5/16" looks right but the "18" threads per inch looks more like 21 or 22.
I will take it to work tomorrow and make damn sure what it is so I can report back.
At least it will be a nice piece of info here on the forum.

5-90

SAE standards for 5/16" threads are 5/16"-UNC and 5/16"-24UNF. It may be ISO - standard ISO threads in that size tend to run M8-1.25 (standard,) but M8-1.0 also exists and is in uncommon use.

M8-1.25 and 5/16"-18 are often confused, and 5/16"-24 and M8-1.0 can also be mistaken.

Thus, having a batch of thread pitch gages (at least!) can be very useful, since that gives you the ability to measure threads quickly and easily - and accurately!

anthonytsi

The thread turned out to be a M8 x 1.25 . Had a guy at a machine shop gage it for me.
Thanks for the advice guys.