Adrian
 
This is an original Crimean tompion for the 1851 rifle and, apart from the diameter differences, is identical to those used in the first 1853 rifles in the Crimea.  I have the brass heads of both types but this picture of a complete one is of another in someone else's collection.  The body is what appears to be a hardwood, I suspect possibly chestnut.  It is split up to the head and secured in position by a pin driven through the brass.  This specimen appears to have what seems to be a slip of leather(?) secured in the slot in the wood.  It is about 4 inches long but I failed to measure it at the time. However a comparison of the relative dimensions with the brass head will give the other measurements.  Tompions that have been buried in the Crimea have lost all their wood to rot except where the wood is inside the brass head.