What screw size/thread do I need to mount picatinny rail to plastic stock?

[jonyork]

Hi Folks,

I have a savage B22 FV-SR which I want to add a MDT Picatinny rail 5" with QD cup.

The rail came with three fine thread screws which I don't think are going to hold nicely in the plastic stock. The Sling stud that is there is a coarse thread one.

Unfortunately, I don't have the means to check the thread pitch, does anyone know what the "standard" coarse thread pitch/screw size for a wood/plastic stock?

Thanks!

 

[BullOnParade]

Without pictures or measurements, I can't be positive what you're referring to ... The sling stud is probably a wood screw style, probably a #10 screw. The fine machine screw thread on the rail is probably a #6 or #8.

 

[Potashminer]

To attach to a "plastic" stock, I think you will need to use screws with nuts, and possibly washers, on the inside - can't see any thread holding through the thin part of a plastic "stock". I have not found any epoxy or glue that will stick to plastic, especially in the cold, so pretty much a mechanical connection would be required. Thread locker on the metal screw threads/nut may help to prevent it from "undoing".

I have not examined the stock on your type of rifle, but most "plastic" stocks have a larger moulded section for the sling swivel "wood" screw to screw into.

 

[fraserdw]

You are going to need wood screws the same diameter as those little screws but long enough to secure in the wood. If I understand your intent to put a rail on a wood stock. If I were doing it, I would tap the rail on the stock where I want to put it to make an outline of the rail on the stock, then I would gouge that area out to secure the rail.

 

[Grizzlypeg]

Is there room on the inside to place a metal plate that you have drilled and tapped for the machine screws?

 

[jonyork]

Here are some pictures!

my thoughts are, I need a similar sized screw to replace the stud one, and 2 more matching to mount the rail.

being that they are coarse thread, I need to pre-drill to a smaller size and screw right in.

Just need to figure out what screw it is and pitch, and get one with the same screw length as the stud one.

Or am I crazy?

 

[New Camper]

Here are some pictures!

my thoughts are, I need a similar sized screw to replace the stud one, and 2 more matching to mount the rail.

being that they are coarse thread, I need to pre-drill to a smaller size and screw right in.

Just need to figure out what screw it is and pitch, and get one with the same screw length as the stud one.

Or am I crazy?

Potashminer is on the right track: I am assuming you have a rail mount bipod... The sling swivel stud is probably in a reinforced pocket: you might get lucky in the screw holes lining up with other reinforced/thick areas, but that will require taking the stock off to examine and determine if coarse threaded wood screws like that swivel stud is even viable. I'm guessing not as I expect you will be hitting thin spots in the stock: This isn't a big deal as you can measure the machine screws provided with the rail and purchase identical size (they appear to be #8 or #10 and typical thread is 32tpi but without measuring one cannot be sure) screws, but longer as you will need a nut and washer on the inside to prevent forces on the rail pulling the nut through (or if you gambled on just using wood screws and my suspicion is right, the threads strip out of the stock). Some stores have a gauge table with labelled nuts on the wall by the screws so you can determine what you actually have and purchase accordingly. Otherwise physically measure diameter and pitch gauges will reveal tpi. If you end up having to go the through bolt method, the only thing that'll matter is machine screw length and does it fit the hole in the rail: package will show you size and tpi: buy matching nuts and washers.

This link will help you: https://www.boltdepot.com/fastener-information/machine-screws/machine-screw-diameter.aspx

Whatever way you go, you will need appropriate size drill bit for drilling pilot holes for wood screw, or through hole for machine screws. Judging by your questions: Yes, pilot holes for wood screws must be smaller than the diameter of the thread... for screws that size, 3/32" smaller should work. Machine screw holes will be just large enough for the fastener to slide in with light resistance.

 

[Potashminer]

It seems in the first picture shown in Post #6 by OP that he has three taper headed machine screws with flat and widened "backing plates" that appear threaded as "nuts" for those screws. Both shorter and longer screws shown - looks like heads would recess nicely into that "rail". I think you have there what it is that you need??? Just need to dismantle the arm and inspect inside the stock where the rail will get mounted - drill three holes exactly on that seam on the stock and done?