This watch strap is designed based on the Seiko waffle strap from the seventies. The original strap was for 19mm lugs, a size that is hardly used anymore.
This strap is for 20mm lugs (made like the 22mm version, with cut out sides at the lugs) and it has a steel keeper.

The strap wears extremely comfortable, not only because of the material (silicone), but also because of the design of the inner side which makes it more flexible. There are holes in the strap that allow sweat to go away. The lug-holes are made for the fat Seiko push pins (use some hand-soap on the tip of the push pin). Because of the free metal tubes that are added to the strap (to be inserted in the lug-holes) it is also possible to wear this strap with standard push pins. The steel keeper is half the width of the rubber keeper that the standard SKX013 strap has, so it does not press much into your wrist, it will also not break but that is a no brainer.

The short end is 7,7 cm, the long end is 12,5 cm. The thickness is 2,6 mm.