Joined: Feb 2012
Posts: 19,344
Likes: 5,461
From: Rochester, NY
Bikes: Stewart S&S coupled sport tourer, Stewart Sunday light, Stewart Commuting, Stewart Touring, Co Motion Tandem, Stewart 3-Spd, Stewart Track, Fuji Finest, Mongoose Tomac ATB, GT Bravado ATB, JCP Folder, Stewart 650B ATB
First- There is no M4 5mm. M4 is a 4mm OD.
Second- do check the boss's shape and it's compatibility with other shift levers.
Third- A bottoming tap will tap to nearly the base of a blind hole, which is what a boss has. Generally one uses a tapered tap then a plug tap and then the bottoming one.
Do be careful with the tap contacting the bottom of the hole. Tap breakage is very easy. Andy
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AndrewRStewart