To create some differentiation between the 5131J-001 and 5131R-001 I outfitted the "R" with a burgundy strap from Patek Philippe. I've commented on previous posts that this combo pairs wonderfully with a Cordovan Shoe and Blue Suit. Attached are some close-ups of the strap. Sorry, I'm not the best photographer because I use a iPhone without any fancy attachments. Lol. There is no reference number on the strap ... only "Patek Philippe Geneve" impressed on one side and the Calatrava Cross impressed on the other.