Thanks for your responses
My cartridge is a Soundsmith Carmen mkII the TT is a Merrill Heirloom and the tonearm is the Classic Six that does not have the micrometer .
When using an Azimuth gauge/block to check the tonearm and cartridge parallel orientation to the record the difference between a 140gr and 180gr is very small , I would say that it would be less than 1mm , but this has caused me to think about trying a 1mm mat and setting the arm for a 140gr record and using the mat for heaverier records bring the two just a little closer . Will a 1mm mat withstand the use of being placed on/off frequently ? If you watch Peter Ledermann's video on SRA I am probably close enough with leaving my setting using a 160gr record .