You need a good strap wrench.the best I came across was a type and you'll see it illustrated, that was made in the USA and has s mall rubber type suction pads. The thread is relatively fine for the diameter and removal of the bezel from the case by unscrewing is not always easy. The bezel of the 80mm diameter (3') chronometric has a rim with an 80mm x 0.9mm thread. This could be the last post from me for the year and it is an item long overdue from me to add to the several posts I've done on the Smiths chronometric speedometer and tachometer.
