What threads for screw holding grip to lower?

I'm trying to finish my first lower build. I started with a double D lower and PSA lower kit. Things were going well until fastening the pistol grip to lower.
The screw (bolt) PSA's kit had was a 1/4-20 x 2" with a hex head (seems kinda crude for a firearm) I finger-screwed it in until resistance about a half-inch down then backed it out and internal threads on lower looked finer than 1/4-20. So it looks like either DD or PSA was wrong.

I loosely tried 1/4-28 and some metrics I had around but still didn't seem to go smoothly.
I have metric and SAE taps, just wondered which I should use.

Suggestions?

Thanks

Why don't you PM or email the owner of the company........ He's a member here. I'm sure he'll answer your questions.

Unless you got the one and only fucked up lower, the lower specs are correct.

Sent from my teepee using smoke signals.

Disregard, I found some plans on line that say it should be 1/4-28

http://www.biggerhammer.net/ar15/cad/ar15_receiver.pdf

Quote:

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Originally Posted by whitbaby

I'm trying to finish my first lower build. I started with a double D lower and PSA lower kit. Things were going well until fastening the pistol grip to lower.
The screw (bolt) PSA's kit had was a 1/4-20 x 2" with a hex head (seems kinda crude for a firearm) I finger-screwed it in until resistance about a half-inch down then backed it out and internal threads on lower looked finer than 1/4-20. So it looks like either DD or PSA was wrong.

I loosely tried 1/4-28 and some metrics I had around but still didn't seem to go smoothly.
I have metric and SAE taps, just wondered which I should use.

Suggestions?

Thanks

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Rule of thumb.. PSA vs anything else.. is always PSA's fault.

Throw that away..get this type http://www.windhamweaponry.com/shope...#axzz2q2bdCQ00
Bowers Tactical carries them I think.

1/4 28 TPI.
Before you go willy-nilly running a tap down it do this: get a 1/4 28 screw with a long threaded shank. Run it down the PG screw hole from the INSIDE Of the receiver. Make sure to oil the hole and threads well and go slowly. When you feel resistance back off a 1/4 turn and then turn it down again.
This will usually "chase" the threads and clean them up without cross threading.

Got it guys, thanks.

I'm thinking someone at PSA (or their supplier/bagger) fancies himself a comedian.
The 1/4-20 x 2" bolt they sent was zinc plated and even had a 7/16" hex head...like something out of a snow blower.

I sent PSA a nasty-gram, not that they ever answer their emails.

Thanks again, and my apologies to DD Jay if he still follows this forum.

P.S. I haven't done anything 'willy-nilly' since I got married.

;->

The usually helpful biggerhammer.net website still misidentifies that thread as 1/4-20 and the contamination runs deep throughout the interwebs.