Interesting artifact
 

My in laws have had this "nut" for many years, and were told it was part of a Rolls Royce.
http://i518.photobucket.com/albums/u...ps59494a9f.jpg
It was gifted to me, to find out what car (?) it was from. A little but of research turns out it is in fact a designed to keep the propellor on the front of a Short Stirling engine, and was priduced in the De Havilland factory in Broughton, Chester. Similar thread here from someone else who has a couple.
Spitfire Landing Gear

Amazing what turns up randomly !