The module corresponds to the module holder for glassware with ST14, but is also equipped with a rotable locking ring that protects glassware with standard joint ST14 against falling out.

Note on joint tolerances for ST14
Maximum outside diameter at the narrowest point of the cone joint: 17.2 mm (larger diameters are too wide for the holder and cannot be held)
Minimum outer diameter at the widest point of the cone joint: 18.0 mm (smaller diameters are too narrow for the holder and would fall out)