It is 35mm.
Presma does not provide the barrel nut thread pitch or the specific tang height besides stating it is low profile. I would recommend reaching out to them directly for more information.
This Presma DPMS .308 M-LOK Series Slim Free Float Handguard should fit and function as intended on your Bear Creek Armory 308 upper. Its designed to fit low profile DPMS pattern 308 uppers.