So to take this further down the rabbit hole..... I got curious and measured mounting screws from a sample of my German pre-98 series rifles - 71, 71-84, 88. All three models use the same .25" diameter and 22 TPI thread pitch. Lengths, thread lengths and head diameters vary. My pre-Gebr. Mauser, Royal Oberndorf Arsenal Dreyse needle gun uses the same .25" diameter but the thread is about 20TPI.