Just been informed that from now on the ZRC straps are not available from stock in 17mm, presumably that would also apply to 19mm, which is also an uneven number. 

773 are no longer available at all although not in the current catalogue I did try ordering some but to no avail. 

This 534 Texas calf especially in the lighter colour with the contrast stitching can be used in 18mm watches, and although compressed somewhat at the lugs, looks reasonably ok. They're a terrific strap, nice padding, leather backed and taper conventionally. Shown here is a recent repair fitted with the 18/16 tan 534Texas Calf. Coloration is not too far off an original Smiths supplied one.