Look on Giacomo web site and click on the parts lists and diagrams. MX shows a pic of the top lever and it is listes as #5203 which is for TMX. Click on the TM list and they have a seperate picture of "old style Top Lever #103" which is for the TM-1. Bill
You cannot tell without tapping the lever up high enough to measure, or if familiar with their two sizes, physcially SEE the shaft. You *can* tap the lever up high enough to peek, but you run the risk of launching parts #117 (spring) and #5109 (pin) which are both housed in the top of the lever, if you tap it out too far.
The older guns use the much larger diameter levers. I didn't realize this until about a year ago that they, TM's used two different sized lever shafts. I guess I just never had run into the much older guns all these years.
Perazzi does not sell the larger sized diameter levers any longer.
I can't remember, but recently a customer sent me his for repair, and I suggested that he ship it to either Lucio in CA or Doug Braker in MN. Doug charges $150 to fix the pin if that's what broke on it.
I carry the current lever whose diameter is: 0.5515".