wondering if anyone could tell me the size of the shear pin for a 04 2.5 merc? would like to have an extra when selling the motor. Thanks

Pull the prop,measure the legnth of the slot where it sits in the prop,the hole in the shaft for diameter use nails of different sizes to determine diameter.
On my small motors that took shear pins I'd just use aluminum nails cut to the proper legnth,or brass rod cut to legnth