Tab On Parker 51 Inner Cap?

[Flounder]

Today I received this smashing bargain, a laconically described and myopically photographed English 51 with beautifully smooth, generous tipping and a rolled silver cap. I've come across a bit of a surprise while cleaning; a sort of nub or tab on the inner cap. I can't say I've ever noticed one before.

http://i773.photobucket.com/albums/yy19/flounder2009/English%20Parker%2051%20Aero%20with%20RSilver%20Cap/th_RSilver51InnerCapTab.jpg

Anyone come across this before? It came orientated to the opposite side of the outer cap from the outer cap's clip tab.

Edited September 24, 2014 by Flounder

[Flounder]

I've reassembled the cap, and decided to orientate the inner cap with the tab in the same position it came in. It doesn't seem to foul on the clip. Perhaps it's there to help keep the clip and outer cap concentric?

[Hooker56]

Perhaps it's there to help keep the clip and outer cap concentric?

 

Flounder,

 

That sounds reasonable. I've never noticed the tab on any of mine. The cut-out keeps the clip positioned as it should be. Maybe the tab was added to keep the circumferences of the clip and cap (as you said 'concentric') from any lateral movement so that it is further 'locked' in place and won't loosen.