Helios 44m lens mount

[goinggreynow]

First off, apologies for not posting this under the existing "Helios 44" thread but being a specific question, I thought it might get a bit lost.
Very simple question really. I have a Helios 44m which I am keen to use on my m4/3. I have searched and understand that this lens came in 3 mounts; M42, M39 and Pentax K. Although I have no first hand experience of any of these 3 mounts, the fact that it has a threaded connection to the camera body (not bayonet) means I can discount the Pentax K.
I appreciate that the most common mount is M42 but before buying an adapter, is there any way of definitely ruling out that it could be a M39?
THe only wording on the front of the lens is Helios-44M and 2/58. On the opposite side of the lens is a small mark, rather like a trapezoid with an angled line through the middle.
Thanks

 

[kendo1]

Measure it

 

[stupar]

I could be wrong but i think all m39 lenses were silver in colour whilst the more common m42 counterparts are black.


I cant remember if the number denotes the thread diameter or its pitch.

I will hedge my bets though and say you have an m42 derivative.

 

[Canon Bob]

Just checking that you're aware that M42 is 42mm and M39 is 39mm?

Bob

 

[goinggreynow]

I could be wrong but i think all m39 lenses were silver in colour whilst the more common m42 counterparts are black.


I cant remember if the number denotes the thread diameter or its pitch.

I will hedge my bets though and say you have an m42 derivative.

many thanks for the reply.

Just checking that you're aware that M42 is 42mm and M39 is 39mm?

Bob

Thanks, Bob. Having zero experience of M42/M39, I had no idea that these numbers represent an actual dimension! Seems obvious now that you point it out - but I didn't know.
I've put a ruler across the screw thread on the Helios and it is much closer to 42mm than 39mm, so I'll assume it's an M42 fitment.

 

[kendo1]