What is the maximum open jaw size of the 99-078 Bostitch 6" Adjustable Wrench? Support October 03, 2020 18:16 The max open jaw size of the 99-078 Adjustable Wrench is 3/4". Related articles I require a Material Safety Data Sheet (MSDS) for a Bostitch product. How may I obtain one? Comments 0 comments Please sign in to leave a comment.