Hi - this was found on the site of T.E. Lawrence's secret desert camp in Southern Jordan. We know he camped there twice, in 1917 and 1918, and that the vehicles involved in attacks made from this location were early Rolls Royce Armoured cars - the so called "Rubies of the Desert".
We think it might be a tyre valve cap, but would really appreciate confirmation of this or suggestions as to what else it might be. The inside is threaded and the scale is mm. Many thanks in advance. Roger Ward