Seiko Series 5 Automatic Grey Dial Men's Watch SRPE51K1 have the caliber number 4R36. Seiko Automatic Men's Watch. An exquisite pick for fashionable Men is this Casual Watch from Seiko. Lending you a stylish look all day long, this watch will impress you with its beautifully done with a Round shape and trendy band. This is specially designed for Men.