The two halves (12,18) of a die for injection moulding of plastics are closed by bolting arrangements (50) which lock on to guide rods (24). The guide rods (24) are attached to one half (12) of the die and pass through holes in the second half (18). The bolting arrangements (50) prevent the guide rods leaving the holes in the second half (18) and thrust device then force the second half (18) against the first half (12). Also claimed are locking devices using a plate which engages a groove (32) in the shaft (26) of the guide rod and one or a number of hydraulic cylinders to provide closing thrust as well as an opening force.
