Rigging screw M12 Right/Left threaded

Rigging screw M12 right/left threaded

Rigging screw in M12 with one right-hand and one left-hand thread. Original number BS-8170. The same screw in M10 is article 4020146. No length or material is stated for it.

What the opposed threads are for

With one thread cut right-hand and the other left-hand, turning the body draws both ends in or lets both out at once, so the length can be changed with the ends still attached. That is what makes a rigging screw an adjuster rather than a plain fastener. Set it so both threads are engaged by a similar amount instead of running one out to its last turns, and lock the setting once it is right so vibration does not take the adjustment with it.