This is an option which is typically used to fasten components to a base (typically a T-slot table) in cases where the component cannot be bolted directly.
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 above the clamps have a hole for M16 bolts ( ICI-16 )