Muhle R41 handle thread?

Does anyone know what the thread spec is for a Muhle R41?
I am embarked on a silly project to make my own custom handle, and I'd like to tap it correctly.

For those who are curious, I have an antique faux-ivory handle from a nail file and I'm trying to drill and tap it to accept the R41 head. Possibly with a brass insert for strength. Thank You,

Can't help you, but am going to follow the progress. 

Well I did a Google search and confirmed at my local hardware store, it seems to be an M5 x 0.8 (whatever that means).

Keep us posted on the progress of your interesting project.

You may want to check out Bob Quinn at Elite Razor.  In addition to brushes, Bob makes handles for Muhle, Merkur and Edwin Jagger razor heads.  His work is very highly regarded.

https://eliterazor.com/handles-and-razors/