I believe its 1 5/16" but do a search on here to be sure. I've seen it posted somwhere before.

Edit: Just checked my tool box the wrench I bought for the job when changing mine is a 1 5/16" combination wrench.

 

U are EXTRA AWESOME!!! thanks for taking the time to blog/post. My husky slide caliper from H depot (3 yrs old, moderate use) fell apart just now. Thanks be to AI and good ol' people posting actual knowledge and not selfie duck lip twerking or guy's being silly and sarcastic

 

1-5/16 sounds right

 

It's is in fact 1-5/16"...that's what I used.