Gear box drain plug

[ramwing7]

Can anyone tell me what size wrench I need for the gearbox drain plug.  I don't have the right size and will have to buy one.  Knowing the size will make it lots easier.
Thanks for your help.

[Bess]

Hi,
     What bike do you have?

[ramwing7]

Duh!  Good question.  It's a 1969 BSA B25s Starfire.
Thru trial and error I got it off with a 24mm socket.
Thanks for your response.

[AWJDThumper]

It is 1/2" UNC - you need a 3/4" AF socket or spanner.

[ramwing7]

Thanks much.