This is a mold to cast a sleave for the heating block of the Merlin hotend. Like the cover it should be cast using high temperature silicone. Us a separation agent, the sleave is only 1mm thick and can easily rip.
To assemble drill the holes to 4mm and use M4 screws to keep the mold tight.
Use ABS or any other heat stable plastic if you want to cure the silicone in an oven.