Monkey tools are used to shoulder tenons and set materials for riveting . They are most often used in conjunction with spring swages of the same size . Monkey tools are great for squaring up and upsetting shoulder on tenons

this is forged from 1.25” square material so it can be hand held or used inverted in the vise.  8” long over all. 
They are sold by diameter they are used on. All holes are a 64” oversized to allow for heat shrinkage after the tenon is cooled .