On a power tool, when is it allowable to have a lock-on switch?

• A. If it has momentary switch
• B. If it has a constant pressure switch
• C. When the blade shank is 1/4 inch wide or less
• D. If it can be turned off with a single finger motion

Answer: (D)

Lock-on switches are meant to let the tool run without you having to keep squeezing the trigger, but safety still requires you to be able to stop the tool quickly. The best condition for allowing a lock-on is when you can turn it off with a single finger motion. That way you can engage the lock for easier, extended operation, yet you can release it instantly if something goes wrong or if you need to stop quickly.

The other scenarios don’t fit safety needs: a momentary switch won’t stay on without continuous pressure, a constant pressure switch requires you to keep pressing to stay on (no true lock-on), and blade shank width has no bearing on whether a lock-on is appropriate.