I recently acquired a very nice Primus 5 silent burner. There is a date code on the burner riser that ends in 62, so I assume it is a 1962. On the burner there are two sets of numbers, one of which is 1961. All parts are stamped with "Primus" so I assume it is all original. The NRV pip and pump leather were good. It lost pressure while running so I changed out the cap gasket. Hated to do it, since even the gasket said "Primus" on it, while my replacement does not. I am a bit unclear about the Primus-Optimus change over, but it would appear this stove is either the last of the Primus line or the first of the Optimus conglomerate stoves. It burns beautifully.