Die and Tap Question

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Hello,

This may seem like a dopey question, but I have never used a die before.

I used a Tap size 1/4-20 to make a threaded hole.

What size Die do I need to make a fitting bolt? (1/4-20 seems obvious to me but I just want to be sure before I go out and buy a Die.)

Thanks!

 

[Stophel]

You got it. You were right and didn't even know it.

The tap and die sizes refer to the threads. The "1/4" is the diameter of the bolt/hole, of course, and the "20" is the threads per inch (tpi).

The larger the number of tpi, the finer the threads; the lower the number, the coarser. A finer bolt, for example, would be a 1/4-28, with 28 threads per inch instead of 20.

There are also number size screws, which are used very often in gunbuilding. I actually don't know the origin of the numbers or just what they stand for. Really super tiny screws are a size 0, but these are not used on guns. On occasion, something as small as a 3 might be used, but generally, the smallest screws found on guns will be something like a 4-40, which is a fine thread, 40 tpi. Commonly used sizes are 6-40 (the size screws used in L&R and other locks), 6-32, 6-48 (often used on modern guns and scope mounts), 8-32 (the internal screws on Siler locks), 8-40 (also used often on modern guns), 10-32, 12-24, and 12-28.

 

[Zonie]

Don't forget the #10-24 (course thread).

For more information about these number series threads, this gives the outside diameters of the male thread.
(If you measure a unknown bolts diameter and it's a few thousanths under these sizes, your just seeing the effect of the threads tolerance (although it could be metric).)
#12 =.216
#10 =.190
# 8 =.164
# 6 =.138
# 5 =.125
# 4 =.112
# 3 =.099
# 2 =.086

If you are unsure about the thread pitch of a male thread and you have a tap that you suspect might be correct, lay the screw/bolts threads on the threaded portion of the tap. If they are the same, the two will fit like a glove.