This is an option which is typically used to fasten components to a T-slot table, for example when the base rail needs to be perpenducular to T-slots.

ICI-12 For Multi-Rail RM ( 2 pcs )
IC1-12-C For Combo-Rail ( 2 pcs )

Both of these can be used with M12 and 1/2″ bolts.

In the picture on the left the clamps have a hole for M16 bolts ( ICI-16 )