1911 Sight Screw, Metric or Unified

[kalister1]

I bought new sights for my 1911. The screw that adjusts the sights up and down needs to have a hole drilled and tapped into the slide.
My thread gages only go to 32 TPI and the screw is finer pitch than that.
It is either 6 - 48 or metric 3.5 - .6, I can't tell for sure. I just ordered a 6 - 48 tap, who thinks it is Metric?

 

[mikec]

What sights? Have you checked the maker's web site?

 

[smores]

6-48 is a common thread pitch for sight mounting screws. I highly doubt it would be metric... but you never know. The sights should come with directions for installing them...

 

[kalister1]

I can't think of the manufacturer off the top of my head.
Instructions? no luck, just a white card in plastic with a nice picture.

I ordered the 6 - 48 thinking the same way. I'll test a piece of scrape metal before I drill the slide just in case though.

Thanks

 

[smores]

I can't think of the manufacturer off the top of my head.
Instructions? no luck, just a white card in plastic with a nice picture.

I ordered the 6 - 48 thinking the same way. I'll test a piece of scrape metal before I drill the slide just in case though.

Thanks

What style of sight is this? Is it the older style that resembles S&W revolver adjustable sights? As in the sight is pinned into a narrow groove milled into the slide, and then adjusted via the screw?

 

[kalister1]

Yes, it looks like that. The sight base is in a dovetail and the rear sight itself is pinned into the base. The elevation screw needs to be threaded into the top of the slide, that is what I need to drill and tap. The top of the slide has a thin rib, I had to mill that rib down a little. My little mill was not happy

Link to sights

http://www.brownells.com/.aspx/pid=26108/Product/1911_AUTO_ADJUSTABLE_REAR_SIGHTS

 

[fa18hooker]

Yes, the Bo-Mar and it's clones are 6-48...why the gun guys never got into the "common" thread pitches is beyond me...I guess to just make it more difficult. The 48 pitch doesn't improve your sight adjustment a whole lot...it's not like we're talking quarter minute on a 1911!

 

[kalister1]

Thanks all!

 

[smores]

Yes, the Bo-Mar and it's clones are 6-48...why the gun guys never got into the "common" thread pitches is beyond me...I guess to just make it more difficult. The 48 pitch doesn't improve your sight adjustment a whole lot...it's not like we're talking quarter minute on a 1911!

Sometimes you can only thread a hole so deep (so as not to weaken a receiver or slide), so having a finer pitch allows you to get more turns on the screw. There's a reason for everything.

 

[kalister1]

If you go too deep you wind up in the firing pin.

 

[kalister1]

OK, it was a 6-48 thread. I have Tin coated drills at home, they will not even scratch the slide. One of the Machinists at work told me to get a Cobalt drill and tap. The cobalt drill is no problem, MSC has them. I cannot find a Cobalt tap in 6-48 anywhere. I have a Premium tap from Brownell's, High Speed Toll Steel. What has anybody used to tap a slide?