knucklegary explanation is correct.
Once you open the top of Z58/59 ( I used snap ring plier), you can remove internal part easily. To use McClicky as replacement part, you need to modify McClicky switch. Take off outer brass or copper ring 1st. Take measurement of internal diameter of rubber boot. Cut off top half of McClicky plastic thread so it can be pushed further into boot. You need very thin conductive washer which diameter is same as inside diameter of Z58/59 and center hole diameter is same as bottom of McClicky so switch can sit top of washer.
Once you remove old switch out, put washer from top so washer can seat on small ledge inside and McClicky switch next and closed top. I used whatever available in my garage so washer look weird but as long as measurement is correct, it should work. I also use hand tools to cut off on top part of McClicky, it is very rough look. I put the unmodified switch to compare.
Now I fixed partially work Z59 and also I can use this Z59 with higher amperage required drop-ins which were make original Z59 clipping.