Sliding collar piston

Here is an unnamed pen with a piston or syringe filler with a unique feature. The piston is controlled with an external collar attached to the piston rod by a pin. I suspect that it is from early in the screw cap era based on the imprint telling the user to unscrew the cap. I have seen a similar pen on ebay (same filler, different chasing). It was imprinted Unity No 9 Selfil-safety. I saved the picture of that imprint and it is displayed below. Calling a screw cap a safety pen also dates the pen in the early 1910s.

This imprint is from another pen I saw once on ebay that had the same construction but different chasing.
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