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Thread pitch on M81 rear sight screws?

Posted: Fri Sep 20, 2019 3:04 pm
by Fred
The screws holding on the rear sight on my M81 are all buggered up. I want to try to remanufacture them, but they're in poor condition to be used as templates.

Near as I can figure is that they're close to a #6-42. The major thread diameter's .138". They're definitely not 40s and with my calipers and a jeweler's loupe I get between .118" and .120" peak-to-peak for 5 threads. That calculates out to somewhere between 41.3 and 42.3 TPI.

If no one can volunteer the factory pitch, I'll just work the lathe until I find something that works.

Re: Thread pitch on M81 rear sight screws?

Posted: Fri Sep 20, 2019 3:50 pm
by kenhwind
I'm under the impression they are 6-40
Henwood in his book on The model 8 & 81 state 6-40 also.
You might find replacements on eBay

Re: Thread pitch on M81 rear sight screws?

Posted: Sun Sep 22, 2019 1:20 pm
by Fred
Thank you for the reply. I disassembled the gun and a 6-40 does fit in the rear sight nut-plate, but a new screw is pretty loose. An 8-40's too big and no matter how I try a precision ground 40TPI Brown and Sharpe thread pitch gauge does not want to fit the existing screws. No oddball metric pitch seems to fit either. Perhaps my M81 was made on a Friday, on worn machines.

I know I can get some Remington Model 8 replacement sight screws off fleabay, but I'm disinclined to pay $12 a pair. I'd rather spend the time in front of a lathe turning hand wheels. I'm already in the process of re-making a variety of existing parts in different materials so it's no big deal to remake the screws too and I'll fatten them up to make a better fit to the original nut-plate.

Re: Thread pitch on M81 rear sight screws?

Posted: Sun Sep 22, 2019 4:30 pm
by kenhwind
Back when these rifles were made, at least the Model 8 the gun companies made what they calculated to be correct for the purpose, not like today or say since WWII where most threads are a standardized pitch and dia.

So maybe these screws may very well be slightly larger then #6 or actually a fractional size.

Re: Thread pitch on M81 rear sight screws?

Posted: Mon Sep 23, 2019 8:03 pm
by Phyrbird
Fred,
I've tried several solutions for these. They are 6-40. All my factory screws fit a screw checker plate with only minimal play. I've had about a dozen of the 8-81s & all have had no issues w/ factory or aftermarket 6-40s. Even my spare sight mount blocks are the same.
You mentioned your screws were "damaged", they maybe have been replaced with others. I had a similar problem with a Contender barrel that some one put the wrong pitch screw in a mount, Imagine trying to find a 6-48 bottom tap to clean up the threads.
Suggestion: get a 6-40 allen screw, they are pretty hard. See if it will fit, perhaps iron out curled threads. Be gentle, a stuck allen can be kinda hairy to remove. I have cut flutes in an allen at times to make a thread chaser tap, but these are almost too small for this.

Re: Thread pitch on M81 rear sight screws?

Posted: Tue Sep 24, 2019 9:12 am
by Fred
Thanks for further evidence, Phyrbird. I believe I'll be remanufacturing the barrel jacket where I'll add another nut-plate to secure some bases for an extended eye relief scope or a red dot, low to the bore centerline (I was never very good with iron sights). :)

Re: Thread pitch on M81 rear sight screws?

Posted: Tue Sep 24, 2019 10:23 pm
by Phyrbird
Look for it, one of our guys drilled a short rail for the rear sight boss & mounted a reflex sight. A shotgun scope could be mounted the same. BUT you could try the Pachymar mount, the Griffin & Howe, or the Williams mounts. Yes they require drill/tap of the receiver, but the G&H mount helped me ring the gong 8" at 185yds 8 out of 10. Got witnesses too. From the Great 8 Event. Plus the G&H looks downright cool on our Ladies.

Re: Thread pitch on M81 rear sight screws?

Posted: Wed Sep 25, 2019 2:10 am
by Fred
The reflex sight was me in 2014. It was a quick and dirty modified weaver rail to try and eliminate the other sight systems as culprit for poor accuracy, and now I'm looking to do it right on a replacement barrel/jacket. I have a drilled-and-tapped receiver already and the offset scope is the worst ergonomics for me.

Needs to be mounted lower to bore:
Image

Re: Thread pitch on M81 rear sight screws?

Posted: Thu Sep 26, 2019 2:04 pm
by Phyrbird
I can dig it. You are right the "to the left" scope does make for odd ergonomics. But so does straight up ejection. If you come up with a viable option for our Ladies I'm sure there would be lots of interest here. JMB was an innovative designer at worst, we can follow his example.

Re: Thread pitch on M81 rear sight screws?

Posted: Fri Sep 27, 2019 8:55 am
by kenhwind
You could make a Scout type rifle with these. If you took and extra rear sight attaching plate and mounted it in front of the rear sight it might be possible to mount a scope in front of the receiver Scout Rifle or Shotgun style.

Re: Thread pitch on M81 rear sight screws?

Posted: Fri Sep 27, 2019 1:24 pm
by Fred
That's the plan. Add another nut plate for a pair of bases and mount something out front. To be honest, my M81's accuracy is so poor, the red dot at 50 yards is probably good enough. Optics would just make the shotgun pattern more visible and disappointing. Image

I have the same FF3 red dot on a TC Contender carbine and it works just fine on a 10" steel plate at 100yds.

Re: Thread pitch on M81 rear sight screws?

Posted: Sat Sep 28, 2019 12:14 pm
by Fred
Made some progress today.

Image

I've been playing with titanium lately. If they're going to be $14 a pair, there's going to be a reason for it. haha. I'll cut them to length, chamfer and slot the heads when the slitter saw comes.

Re: Thread pitch on M81 rear sight screws?

Posted: Sat Sep 28, 2019 2:38 pm
by Phyrbird
8-) 8-) :idea: :!: :!:

Re: Thread pitch on M81 rear sight screws?

Posted: Sat Sep 28, 2019 3:42 pm
by Bandersnatch
Fred wrote:
Wed Sep 25, 2019 2:10 am
The reflex sight was me in 2014. It was a quick and dirty modified weaver rail to try and eliminate the other sight systems as culprit for poor accuracy, and now I'm looking to do it right on a replacement barrel/jacket. I have a drilled-and-tapped receiver already and the offset scope is the worst ergonomics for me.

Needs to be mounted lower to bore:
Image
I want to do this to one of my .30's.

Re: Thread pitch on M81 rear sight screws?

Posted: Sat Sep 28, 2019 5:43 pm
by Fred
I know I'm deviating somewhat from my own thread topic but I could make a few aluminum "universal" picatinny red dot bases for the forum members if there were interest. I don't have anodize or Cerakote at my disposal so there'd be an extra step somewhere to make it a uniform color. Judicious application of the "Anodize Pen™" may be required to make it a uniform color. :D Or I could get a set Cerakoted locally.

Of course if the Forum Admins object, I wouldn't solicit...

Re: Thread pitch on M81 rear sight screws?

Posted: Mon Sep 30, 2019 8:11 pm
by Phyrbird
I'm in

Re: Thread pitch on M81 rear sight screws?

Posted: Tue Oct 01, 2019 8:45 am
by Bandersnatch
I'll take one.

Re: Thread pitch on M81 rear sight screws?

Posted: Sat Oct 05, 2019 6:32 pm
by Fred
Slitter saw showed today, so I made an arbor and finished my screws:

Image

I'll order some material and make half a dozen little Picatinny adapters for the rear sight hardware. I'll post up in the for sale forum in a few weeks.

*edit* here's the for sale thread:
http://thegreatmodel8.remingtonsociety. ... f=4&t=5620