A mast traveller should not jam during hoisting and lowering of the sail. One easy way to achieve this is to make them in one piece, such that when tension is on the halyard, the ring is held in a horizontal plane, or at least at right angles to the line of the halyard. The ring itself does not have to be that strong, since it is the halyard that is taking most of the load when sailing. We offer these in bronze, leathered or unleathered. Please note that in all cases the traveller is dimensioned for a spar diameter - so a “70mm” mast traveller has a ring of 100mm id, for example.
If nothing seems to be going in the basket, see here