I've lost the brass colored cap that goes with my rod tube. All I can calculate is the minor diameter of the threads which is roughly 1.630" - can someone tell me what the OD would be? Thanks.

On a standard unified thread, a 1.630 minor correlates with a 1 11/16" thread. Unable to help much more than that without more info or seeing the actual thread.

Tim,

Here is a formula you can use to find the OD threads for you rod tube cap. You will need a thread pitch gauge. You can pick one up at good hardware store. I would suggest to pickup one each for inch and metric threads.

Here is what you need to measure first. With your thread gauges find the thread pitch. Lets say it is 20TPI. You now need to divide 1” by the pitch. 1/20=0.05
Now the constant used for standard “V” thread depth is 0.866. So 0.866 X Pitch = Depth.
Ex. - 0.866 X 0.05 = 0.0437 Thread depth. All you have to do to find the thread OD is multiply the thread depth by two and add the ID of your tube threads 1.630. Ex - 2 X 0.0437=0.0874 + 1.630=1.7174 Thread OD.

Note Metric threads are easier. The pitch is all ready in a useable form. You don’t have to convert fractions. Ex. – 1.5mm pitch equals 1.5mm distance from thread to thread.

Better yet I would find a local machine shop and ask them for help. Most the ones I know will take time to help you with charging you.
You may also call REC. They sell tubes. I haven’t tried but they may sell you just the cap for your tube.

David Cockerham