Hello Miguel,
in the HDv481-73 dated 1938 there is this round - 3,7cm Sprgr.Patr. 18umg. mentioned and they give
3,7 cm Kpf.Z.Zerl.P
3,7 cm Kpf.Z.Zerl.P MP - with the Zerl.P dashed out
3,7 cm Kpf.Z.MP
Only found in the HDv481-51 3,7cm KWK additional pages dated 25.4.39 and they mention the AZ 39 for the 3,7 cm Sprgr.Patr. 18umg. KWK and for the 3,7 cm Sprgr.Patr.40 KWK
So I guess for the early Sprgr.Patr. 18umg. you need one of the 3 above mentioned fuzes and for the later than 1939 rounds the AZ 39
Erik