The piece in question is a Meisterstück Safety pen model 20 of hard rubber, one of the most common early models. The cap is by design the most vulnerable component; turning a new cap lip from old material is laborious and economically hardly worthwhile, since the collector value of a complete model 20 is not exceptionally high. On Safety pens, after filling, the nib is retracted before the cap is screwed on so that no ink emerges. The sealing surface lies at 45 degrees on barrel mouth and cap top; if both are undamaged and the cap is firmly screwed on, the pen is tight. For cleaning an ultrasonic bath is suitable. The cap edge can alternatively be turned in silver if hard rubber is hard to obtain.