Re: Colt 1908 .25
The spring guide is 19.37mm long. The body diameter is 2.58mm and the head diameter is 4.28mm. The firing pin itself is 27.8mm long and 6.34mm in diameter; the internal hole is 4.69mm in diameter and 18mm deep.
Remember if making that firing pin that the small (front) end has to be long enough to act as an ejector. If too short, the gun will fire but the empty case will not eject.
FYI, the firing pins, springs, and spring guides for the Colt Vest Pocket 1908, the Browning Model 1910, Browning Model 1922, and the FN Model 1906 are all the same.
Also if making a spring and guide, remember the groove under the guide head and crimp the last coil of the spring, then expand the first coil so it is tight in the firing pin. That keeps the whole firing pin, spring and guide together as an assembly when the gun is disassembled.