3/8" x 24 TPI is a UNF (Unified Fine) thread tapping drill is 8.5mm
5/8" x 24 TPI does not exist in anything I can find the nearest UNF thread is 5/8" x 18 TPI tapping drill 14.5mm

(See Andrews reply below – 5/8" x 24 is probably UNEF – not a size I've come across before)

Threading a bar just start with nominal size so 3/8" dia and 5/8" dia.

3/8" an 5/8" BSW or BSF are much coarser than the TPI you have given. The nearest metric threads would be
10mm x 1 IsoMetric Fine and 16mm x 1mm IsoMetric Fine. Tapping 9.2mm and 15mm drill respectively.

If you are making both threads, internal and external unless there is a good reason ie matching existing kit just go for what you have or can easily get hold of. I would go for standard IsoMetric coarse as these are the easiest to get these days (unless you are in the States) but don't know if you can alter the bar sizes to suit?

John

Edit: Add ref to later post

Edited By Journeyman on 19/05/2021 09:28:43

You have not said what thread form you are using.

For Whitworth threads (55° ) with this pitch the thread depth is 0.02668". Subtract twice this from the outside diameter to give the core diameter. The tapping drill should be slightly bigger than this.

For Unified threads (60° ) the figure for internal thread depth is 0.02255".

So for Whitworth that gives 3/8- (2×0.02668) = 0.32164", 8.17mm. So Ø8.2 or slightly larger. 9mm may give a weak thread but be easy to cut, it depends on the material, how easy you want the thread cutting to be and what loads it is being subjected to.

Repeat as required for the 5/8 and similarly for Unified if that is what you are using.

Martin C

Smileys again!

Edited By Martin Connelly on 19/05/2021 09:22:49

Yuk! Depends what type of stainless, but most likely austenitic, ie, the 3xx series. Of these 303 and 316 are easy to machine although 316 has a propensity to work harden, but avoid 304 as it's 'orrid stuff. For tapping in stainless steel I drop the thread engagement to nearer 50%, so that gives 8.9mm for 3/8" UNF and 15.3mm for 5/8" UNEF. For external I'd definitely screwcut. But if dies must be used then ensure that the die is rigidly aligned with the work, at least to start with. Trying to start a die by hand in stainless steel is a receipe for disaster, or at least wonky threads.

The SO239 connectors are a blast from the past, must be 40 odd years since I've used one.

Andrew

Boring the hole may be cheaper still

I've not tried it yet as I have not had the need, infact I don't find I thread cut a lot in the lathe so even less likely to need it with something set up on the mill. But if a job comes up where it's needed would not mind giving it a go.

I have spiral milled a few holes but again if the item is on the lathe then may as well just bore it at the same time. For example last week I did the piston for an IC engine the underside of which had a circular bore to form the skirt and then two other pockets beyond that shaped to suit the wrist pin, I did do the CAM for the circular bore but ended up doing it on the lathe while I was turning the OD and just doing the two odd shaped deeper pockets on the CNC

Chris I find this chart very useful *link*

http://pages.cs.wisc.edu/~bolo/workshop/thread.html

H

Still standard fare on almost all modern Ham Transceivers , not only on the HF Antenna connection, but even on VHF and UHF – in fact, the SO239 was known as a UHF connector..

I don't recall the SO239 being used much above a couple of hundred MHz due to non-constant impedance through the connector. Above 300MHz we used BNC and SMA, or waveguides!

Although the SO239 is labelled as a UHF connector apparently that is because it was developed in the 1930s when UHF meant over 30MHz, not the modern definition of UHF as 300MHz to 3GHz.

Andrew