That small cross hole is a feature on many commercial Mauser cocking pieces with the flat bottom. Many of the military cocking pieces with the double "V" slope on the bottom won't have that. For the flat bottom type, there is a couple finishing nails laying on my shelf to use on them. For the military type, is probably several ways - I have a length of shoe lace - kind of like a "figure eight" - one loop goes around my wrist and other smaller loop slips over the face of the cocking piece - that lets me pull back with my arm and leaves my fingers free to manipulate the shroud - no doubt others have different ways to do that.
On a P-14 or M1917, you will find they have a "hook" on very rear end of that cocking piece - makes it even easier to disassemble that firing pin assembly - I use a split key ring around a finger knuckle to grab that hook to pull back and unscrew. I think a WWI soldier could use a boot lace or similar. That, and the design for single round feed, are two of the few true improvements that I have come across over the 1898 Mauser design - most all other "improvements" give up some function or are cheaper to produce - usually giving up some function.
Once the innards of the bolt are unscrewed, I usually place the firing pin vertical in my wood worker vise - and clamp the lower (forward) 1 1/2" or 2" (3 to 5 cm) of it. One hand pushes the bolt shroud straight down to compress the main spring, and the other hand gives that cocking piece a quarter turn to release it from the firing pin notches. Seems to be about the same for various m95, m96, m98 Mausers and P-14 and M1917 Enfield rifles.
