How to identify an internal thread

[Robotstar5]

I have the kit to measure/identify male threads, but don't know how to measure/ID an internal thread and no I don't have a huge selection of assorted bolts to try in it, well actually I have a fair selection but none of them fit so how's done?.

 

[Seadog]

Usually with a thread gauge, which you say you have. Measure the ID with verniers and then you have some idea of what you're looking for. The Zeus chart is usually good for the common thread sizes.

 

[brightspark]

thread pitch gauges are pretty thin and will get in unless its a small hole

 

[Robotstar5]

thread pitch gauges are pretty thin and will get in unless its a small hole

It's only about 4-5mm diameter and my thread gauges are too deep to fit

 

[Pete.]

Screw a piece of wood into it then measure the pitch with your thread gauge against the oily marks left in the wood.

 

[MattF]

Seeing the thread title, it's hard resisting saying: "If it's on the inside, it's definitely internal". Pete's suggestion will work well. A piece of tight fitting dowel, and you're sorted.

 

[merryman]

Best of luck if it is that size as 2BA, 3/16" Whitworth, 3/16" BSF, 10-32 UNF and 10-24 UNC as well as 4 and 5mm are all in the frame.

 

[brightspark]

whats it on and what material

 

[Welderpaul]

It's only about 4-5mm diameter and my thread gauges are too deep to fit

Drill it out and tap M6 then you will know which thread it is with certainty

 

[rikrobson]

If you have an assortment of taps lightly try them in the holes. Taps have the thread written on them

 

[Carl Wilson]

What is it on? That can often be a clue. For example instrumentation kit of British manufacture through to the 70s often uses BA threads. Ok not exclusively but it's a start.

 

[Robotstar5]

What is it on? That can often be a clue. For example instrumentation kit of British manufacture through to the 70s often uses BA threads. Ok not exclusively but it's a start.

1960's Wipac magneto cover, I will have to post accurate measurements when I can get to the workshop.

 

[graffian]

As said above knowing it's Wipac narrows it down. You could even look up parts list, does[did] Wipac use BA?
~4mm core is probably 2BA.
So get a 2BA screw and try it in the thread.

 

[Carl Wilson]

Agree. British 60s electrical could very well be BA. And the sizes you are talking indicate 2BA.

This sort of thing is rather like detective work. Look at the clues and narrow down the likely possibilities.

 

[Robotstar5]

I found my tin of "will come in handy one day" assorted fasteners and identified it as 2BA so will get a couple ordered, also found the tapped holes in the cylinder barrel that hold the tinware are metric M6 which surprised me on a 1960's British engine, but may have been modified by a previous owner? @Welderpaul

 

[Hopefuldave]

6mm major diameter 1mm pitch but funny flank angle (47&1/2 degrees included) would be 0BA...

Dave H. (the other one)

 

[Robotstar5]

6mm major diameter 1mm pitch but funny flank angle (47&1/2 degrees included) would be 0BA...

Dave H. (the other one)

M6 bolt runs in OK until it bottomed at about 20mm engagement so I think it's probably M6?

 

[Hopefuldave]

probably a boroughly thuggered 0BA then... Stick an M6 in to take up the slack

Dave H. (the other one)

 

[Robotstar5]

As said above knowing it's Wipac narrows it down. You could even look up parts list, does[did] Wipac use BA?
~4mm core is probably 2BA.
So get a 2BA screw and try it in the thread.

If I could find one, I've spent quite a while surfing the interweb but no luck yet if anyone knows where to find drawings, parts list etc. for a Wipac CJ1218 or 1219 magneto I'd be grateful

 

[Carl Wilson]

Have you tried looking at stationary engine forums? I understand these magnetos were often used on them.

I asked my brother for you. He got into engineering as an auto electrician. He advised trying the stationary engine people.