Just wondering between 3/4 or 5/8 
3/4 tooling started in wood working over 100 ago and is still the most popular hole size for dogs, pins, clamps and holdfasts. The 3/4 was for woodworking benches because of the strength and accessibility of common shop materials like, bolts, dowels, and drill bits to drill the holes. Early tables had square 3/4 holes that could be made from glueing 3/4 thick boards together with spacers. So the holes were easy to make and the tooling was plentiful.
3/4 for welding tables are done for the same purpose. It’s large to make strong tooling, 50% more area than 5/8. More surface area on the ball bolts to not damage the table surface. Stronger pins for more clamping pressure. 3/4 and 19mm are the same size. Woodworking and metal working can share the same tooling because that is the standard.
Theres not one engineering benefit to 5/8 hole over 3/4. For example our double dragon clamp wouldn’t work well in 5/8. Along with many other fireball designs. The 3/4 opens up more fixture opportunities than 5/8. Both the metal trades and working can benefit from each other.
Fireball doesn’t want to be constrained by a hole diameter that limits designs. The old timers got it right 100 years ago, 3/4 is mathematically the perfect hole size.