From CCP4 wiki
The crystal sits in the loop, the loop atop a pin, which is attached, usually with superglue, to a base (most frequently magnetic). Hampton calls the whole assembly CrystalCap. Caps protected by a vial can be stored in liquid nitrogen.
Potential problems after mounting the cap onto the goniometer head
- ice crystals at the bottom of the base - These will slowly thaw and move the loop away from the cryostream ==> use only dry caps for freezing crystals
- loose pins in the base => superglue pin into base and let set before freezing
- magnets too weak (base too heavy)
- magnet too strong, leading to whiplash effect and catapulting the crystal from the loop (when freezing crystals directly on the beamline, not when mounting prefrozen crystals)
- incorrectly fastened goniometer, magnet etc.