My old watch strap was beginning to get a little rough round the edges so I decided to make a new.
The watch I have is a Omega Speedmaster so the lug width is 20 mm. I cut the leather 2 mm oversize. This was maybe a bit too much. The upper part is made from 1 mm leather and the liner is made from skived down pig skin. I think the thickness was round 0,5 mm. The fillers was made from 2 mm thick leather.
2 mm bicycle spokes was used:
8,5 SPI with Fil au Chinois 632 in white