Parker 51/61 prototype shop model fountain pen. This is a true prototype shop model pen from Parker’s Janesville factory. The cap is unique, with a clip similar to that of a 61 and the top of the cap similar to a Varsity. It has a black enamel strip that runs behind the clip and extends to the base of the cap and is marked PARKER on either side of the strip. The cap is also marked I-P-5300 10-17-57. The barrel is equally strange, it has a Vacumatic nib with a slight threaded section. The cap will thread just over one quarter of a turn onto the barrel. The barrel itself comes apart near the top where the internal threads are visible but also near the base where the lower threads are visible. If unscrewed at the base the entire filler unit comes out and shows a cutdown version of a 51 Aerometric filler with a plug and tube coming out where the pen could be filled without having to immerse the nib in ink. Length 5 1/2” posted 6 7/16”, filing mechanism is prototype Aerometric fill. Overall excellent condition, a special Parker prototype.