Grub screws in uprights

[mark]

Just one m6 should be sufficient, my iva tester was happy with that

You dont dont want to be drilling too many holes in your uprights!

The mushrooms are well and truly clamped in position by the pinch bolt anyway, the secondary fixture is just belt and braces

As Ronnie says set bolts are generally a higher tensile strength should you feel the need to go one better than an ordinary bolt