Cartridge mount screws - stainless steel


I need longer mount screws to mount my cartridge, can i use plain steel screws or must i use stainless steel screws . I am having a hard time finding small stainless srews, 20 mm long locally.
tshulba
Here is one option. 2.5mm x 20mm stainless socket head cap screw. 12.59 per pack of 50 from McMaster-Carr. Have enough to hand out to friends!

Punch in this part number:

91292A019
Is 2.5 -20mm the right size for Shelter 501 MKII?
McMaster-Carr does not have metric sizes brass screws.
Any other sources fro brass?
I was not able to locate stainless or brass screws today at least not 20 mm length only shorter ones, they told me they weren't available from the supplier. I purchased a die and made my own brass screws on the lathe , took about .5 hr.
Mounted up the ZYX Airy 3 on the Graham Phantom with the spacer they provide now i have to re-adjust everything.
I had to install the spacer under the cartridge cause my VTA was as low as i could go and i needed to lower it more.