You will need this adapter for the Sig MPX .177.
https://donnyfl.com/products/sig-mpx-1-2-x-20-adapter-a52?_pos=1&_sid=1d3a5a8fe&_ss=r
I recommend the Tatsu .177/.22 1/2x20 #S28.
https://donnyfl.com/collections/ldc/products/1-6-x-4-25-inches-tatsu?variant=6781041475623