Aaron McMichael is making a really nice set of pin plates that fit GRS engraving vises. If you're engraving large items, this could be a great solution for hard-to-hold articles. They are beautifully machined with standard size pin holes. He also makes one with through-holes for molding items with Thermo-Loc.
The standard Jumbo Pin Plate sets are $175 and the Thermo-Loc model is $250, and they will fit the GRS Magnablock, Low Profile Vise, and Positioning Vise. They will not fit the GRS Standard Block.
For more info email Aaron directly at email@example.com