Stephens push knob (variation of button filler)

The Stephens pen with its push knob style filler is an elegant version of the button filler. Unscrew the end of the barrel. It appears to be a blind cap, but will only unscrew part way. Then this cap is pushed to press on a standard pressure bar. Laurence Oldfield has a very thorough write up on this pen with far more details (patents, disassembled mechanism, etc). StephensTechArticle (