My feeling has been that Omega added the 5 or 6 to the front of some or all of their endlink models at some point without any change in design.
@pdxleaf and I have examined a number of 11/511 endlinks and while there is some variation between different batches, there is nothing fundamentally different in the way 11s and 511s look. Likewise we’ve spotted some very subtle differences between some BoR bracelets that are considered to be interchangeable, but not enough of them to say the two models have different designs or, as above, different factories had slightly varying specs.
