m305 castle nut grub screw

[marky123]

howdy
Can anyone tell me the allen key size needed to get this off please?
I've a full metric and imperial set and none of them fit...
regards
MARK

 

[Pr589]

howdy
Can anyone tell me the allen key size needed to get this off please?
I've a full metric and imperial set and none of them fit...
regards
MARK

I think it is 1/16" however when I micrometer the SAE allen key that fits my castle nut screw it is 0.0605" in diameter.

 

[marky123]

thanks.was that measurement across flats?

 

[Andy]

It's 1/16", but the key might take some wiggling and pushing to get it. Make sure it's fully seated before you turn it.

 

[Pr589]

thanks.was that measurement across flats?

Yes.

 

[jonh172]

1/16" is the USGI size, some Norincos need a 1/20", like the one I just disassembled.

 

[papy]

And some recent Norinco's (2014) use torxs screw...

 

[krprice84]

1/16" is the USGI size, some Norincos need a 1/20", like the one I just disassembled.

1/20??? Who even has those? You must have a odd collection of tools, sir!

 

[45ACPKING]

the one allen key I have that seems to work on most but is still undersize for many , measures 1.54mm

 

[jonh172]

1/20??? Who even has those? You must have a odd collection of tools, sir!

It's an odd one for sure!
It's some "tooltown" or "harborfreight" set I've picked up over the years. It's marked 1/20 and it fits the slot perfectly!

 

[ipscgraz]

1/20" is actually 0.050"

This is a common size and is usually part of a full set. Not sure if it is the right size for the CN lock screw...I will have to dig a rifle out of the safe.

 

[45ACPKING]

1/20" = 1.27 MM , seems a bit small
1/16" = 1.5875MM
My guess would be an allen key in the 1.6ish MM size is the ticket
Over all these years and a few hundred chinese rifles across my bench (as well as american) I've always known the chinese flash hider set screw to be a larger and not very well defined hole over the american parts.
1/16" fits american made castlenut retaining screws and generally floats in the chinese screw.
At clinics it's always a hit and miss finding the right allen key for "every" rifle present and often we make an easy out when the right tool can't be found

 

[TacticalTeacher]

All depends on which high school shop class put yer rifle together

I'm not joking and I was a high school teacher.

Yeah it always seems to change form batch to batch!

Cheers, Barney.