Spool-Type Insulator, which is easily identified by its shape, is usually used for secondary mains. The spool insulator may be mounted on a secondary rack or in a service clamp. Both the secondary low-voltage conductors and the house service wires are attached to the spool insulator. The tapered hole of the spool insulator distributes the load more evenly and minimizes the possibility of breakage when heavily loaded. The clevis, which is usually inserted in this hole, is a piece of steel metal with a pin or bolt passing through the bottom.

Spool valve has a pressure inlet port, a work port and a tank port. It is responsible for communicating the pressure inlet port to the work port and the work port to the tank port. Spool valve consists of two body segments and a balanced spool shaft. The spool valve is based on a balanced spool design to create a fast 'ON/OFF' fluid dispensing function that is not affected by material input pressure. The valve is designed to be opened by air pressure and closed by a return spring (single acting).