I've got an old bike with a typical pinch-bolt system for clamping the seat pin, usual thing- slot in the frame, couple of ears with holes in and a bolt to tighten. This bike gets used by Ms P and I to go to the shops/ pub etc. and I get fed up of looking for a spanner every time I want to use it so I want to get a 'quick release'. I know you can get such a thing- some older folders have them- but what would it be called?