size of a small screw?
- Thread starter Martin
- Start date
Martin said:How do you determine the size, thread of a small guns screw (e.g. bead).
There are so many different sizes!?
A gauge would be perfect or a kind of metal plate with all threads in it.
Martin
Use a micrometer and a screw pitch gauge or compare it to a known screw. 3 x 56 is usually the smallest and 6 x 48 usually the largest, I guess 4 x 40 and 4 x 48 and 5 x 40 in between... and then some factory sights with no threads, just peened in place.
gunasauras
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Martin said:
40 threads per inch actually...
Martin said:
Nope. #4 doesn't have any direct relationship to a diameter, AFAIK. It's just a number. Works out to about .107, according to my caliper.
You'll find that gunsmithing threads are oddballs, ie you won't be able to get taps at Canadian Tire or Home Depot. 4-40 is no problem as it is a standard thread. But the two most commonly used for scope mounts etc. are 6-48 (as opposed to 6-32, which you'll find in the hardware store) and 8-40 (as opposed to 8-32.) If you need taps for either of those, you'll have to get 'em from Western Gun Parts in Edmonton or Brownell's. You can special order them from industrial suppliers such as Ackland's but they will comparitively cost a small fortune (ie about $25.00 ea.) since they won't be a stock item and may have to be made up.
Stuart
Martin said:
No 4 means number 4 gauge. It is a number used as part of a standard for small screw sizes that was developed by engineering organisations like ASME (American Society of Mechanical Engineers).
Prior to having a set standard, there were many different screw sizes and pitches that existed all over the world making manufacturing/repair difficult unless you could obtain material/parts from the original supplier. So various organisations developed a standard for industry to follow, to simplify things.
In North America there is a series of screw gauges that go from 0 to 30. For 0 through 10 gauge the diameter of the screw increases by 0.013" per gauge after #10 it increases by 0.026".
So when you see something like 6-48 it is telling you that it is a 6 gauge screw with 48 threads per inch.
Mudpuppy said:
Thanks for the explanation. But according to the above, I think my aforementioned #4 screw ought to measure .013 x 4, which is .052. However, I notice that .026 x 4 = .104. And a #6 in front of me measures .161, which is close to .026 x 6 (=.156) ??? I must be missing something obvious here.
StuartFrom the tables:josquin said:Thanks for the explanation. But according to the above, I think my aforementioned #4 screw ought to measure .013 x 4, which is .052. However, I notice that .026 x 4 = .104. And a #6 in front of me measures .161, which is close to .026 x 6 (=.156) ??? I must be missing something obvious here.
Gage --Major diam
0 ------0.0600
1 ------0.0730
2 ------0.0860
3 ------0.0990
4 ------0.1120
5 ------0.1250
6 ------0.1380
8 ------0.1640
10 -----0.190
12 -----0.216
A common number 6 screw is 0.1380"
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