Drill and Tap size for 870 Picatinny rail?

just one more round · **Posted:** Thu Feb 04, 2021 9:37 am

I bought the UTG Picatinny rail mount (MTU028SG) to install on a mid-'90s 870 Express for making it into a Turkey Gun. This UTG rail I bought comes with screws to install on modern 870 Express that are already drilled and tapped. Anyone know the corresponding thread or tap size used on the pre-tapped receivers so I can use the screws that came with the mount?
Thanks,
Mike

CriscoKid · **Posted:** Thu Feb 04, 2021 10:09 am

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Mike, I'd suggest trying to screw one of the screws them into the receiver w/o the base to find out.

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just one more round · **Posted:** Thu Feb 04, 2021 11:21 am

Sorry if I wasn't clear. I have to drill and tap my receiver to mount this rail. I was wondering what the OEM size drill and tap were used on modern pre-tapped models from the factory. The purpose was so I can use the screws that came with the mount.

just one more round · **Posted:** Thu Feb 04, 2021 11:26 am

I think its #6-48. Can anyone confirm?
Thanks,
Mike

F*W*F · **Posted:** Thu Feb 04, 2021 11:45 am

My V3's use 6-48's, and the Redfield bases I used on them are also labeled for the 870.

I also just looked at my factory d&t 870, and the plug screws definitely look smaller than 8-40, the other possible candidate.

So, I'd say 6-48.

Safetyfast · **Joined:** Sat Jul 13, 2013 8:10 am **Posts:** 197

F*W*F wrote:

My V3's use 6-48's, and the Redfield bases I used on them are also labeled for the 870.

I also just looked at my factory d&t 870, and the plug screws definitely look smaller than 8-40, the other possible candidate.

So, I'd say 6-48.

I’m pretty sure that’s the size I used when I did mine. Take it slow and use a good bit and oil.

just one more round · **Posted:** Thu Feb 04, 2021 3:23 pm

Thank you guys, 6-48 I'm pretty sure it is; and thanks for the pictures too. Reminds me, my drill press down as it needs a motor. Allways a "pre-project" to do around here before you get to do the "real" project it seems like.
Cheers,
Mike

CriscoKid · **Posted:** Thu Feb 04, 2021 3:47 pm

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Mike, you might be able to try a mount screw in another gun/rifle that you know has 6-48 screws to confirm.

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oldshotty · **Joined:** Thu Feb 01, 2018 2:38 pm **Posts:** 211

6-48 definitely

Safetyfast · **Joined:** Sat Jul 13, 2013 8:10 am **Posts:** 197

Checked the tap I used on mine and it is 6-48. Used a 31 drill bit but started out with a center drill to make sure the holes were centered.

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Drill and Tap size for 870 Picatinny rail?

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