Seiko Prospex SSC813 Specifications - Lug Width & Strap Size
The Seiko SSC813 watch has a 20mm lug width and is compatible with 20mm watch straps.
The Seiko SSC813 case size is 39mm in diameter and 13.3mm thick.
The Seiko SSC813 has a lug to lug measurement of 45.5mm.