I had this update fully typed then had a power failure!

Starting again.

First I'd like to apologize because I didn't post any pictures.

Here is the shifter boss for my Ross Signature. Current shifters are Shimano Z401. These take a Shimano only proprietary bolt (machine screw?? lever Screw??). I recently acquired a partial Exage Sport groupset which included the shifter set but no bolts. I reached for some spare bolts and no, standard M5 shifter bolts don't work because the Z401 bosses are threaded for a smaller bolt size. I believe that the current bosses are Shimano A type bosses and require bolts that are referred to variously as M4.5 x .75 or 4.5mm x .75. They are ones referred to by JohnDThompson above.



Z401 and Exage Sport shifters



Exage on top and 401 on bottom


The original bolts are a MM or so too short to fit through the Sport shifters and engage the threads of the boss and the Exage require a different boss cover than the Z401 have.



401 base on top and Exage on bottom

I spoke with a local frame builder who suggested that rather than search for longer M4.5 bolts I should just tap the threads to take the M5 x .80 bolts. I would have had him tap it there and then but I didn't have the frame with me. He walked me through the tap process and it seemed straight forward.

I approached a neighbor who has lots of taps and other nice tools but he didn't have any 5mm taps. The neighbor suggested that I insert a drill bit into the bolt hole in the boss and drill into the frame and he said that drilling would prevent the tap from bottoming out and breaking in the threads (at least I think that's what he meant). Judging from the response on here, I guess that pre-drilling before tapping is not needed.

The neighbor suggested a local store to get the tap. I began to wonder if there waa certain thread size that I needed and now realize the .80 part of the M5 x .80 will cover that question.

This brings me to the next part where my post was confusing

The replacement boss covers won't fit onto the bosses and so the bosses must be modified or trimmed to allow the mounting of the new bosses. In his post RCCARDR used a file very judiciously and trimmed the stop so that new covers would work.

RCCARDR photo



As for the drill comment, I found a thread on here where someone taped the frame to prevent damage and used a 1/2 inch hole saw with a 9mm center to very carefully trim the boss to allow the boss covers to fit snugly to the down tube. I suspect I could get by with just the tapping of the threads and a little - very little - filing.

Modification: Old style Shimano downtube shifter mounts to later style

brewerkz photo before




brewerkz during photo



brewerkz after photo