The main feature of this round-bladed knife is the substantial protective guard which completely shields the blade when not in use. A soft pressure pad enables force to be applied when in use, but it does nothing else (on some knives it is used to retracts the blade).
There are two sizes of circular knife generally available. The more common, with numerous suppliers of spare blades, is this size, 45mm. All blades, to our knowledge, of this size are interchangeable between manufacturers.