New forks require new tools - the 38mm seal installer puck is for those new 38mm lower leg seals and is to be used exclusively in conjunction with the RockShox x Abbey Flangeless Dust Seal Installation Tool, threading into the body of the tool like the 32mm and 35mm pucks that tool comes with.
The puck has perfect fitment against the dust seal and crown making it impossible to install the dust seal too far into the lower leg. Plus, it has an extended sleeve that locates the upper bushing, which serves to locate the seal perfectly every time.