Water pump pulley question

[Nigel Watson]

Whilst driving to collect for Remembrance Day last week, my carrier started overheating. It made the driver's compartment nice and warm! I had topped water up and knew there were no leaks so I immediately thought I had broken both fan belts. Pulling over I checked, yes they were off, but no they weren't broken. Then I noticed a water pump pulley lying on the engine bearer. Checked the spindle and it turned fine, no leaks etc. The thing is there is no visible evidence of how it is fixed on. No weld marks, no keeper pins, just seemed to have been chapped on. Does anyone know how they were fixed onto the spindle? Easy fix but want to know how it was originally done.

Thanks