Of course you’re smarter than a bolt, but SmartBolts are still pretty crafty — they can show you if they’re loose, tight, or overtightened. For the average Toolmonger, this is overkill; we’ll break out the torque wrench if we need to know when the bolt’s tight enough. When it’s not critical, the grunt method works — one grunt for tight, two grunts for really tight. However, neither of these methods will show you if a bolt has loosened over time.
When a bolt is tightened, the tension in the bolt causes it to stretch a few microinches. When the SmartBolt stretches, the colored indicator pulls away from the top of the bolt to give a visual indication. Remember, torque isn’t always directly related to tension — friction between the threads from plating, rust, or scale can cause a bolt to require more torque to reach the desired tension.
You can get SmartBolts in sizes ranging from 7/16″ to 1-1/4″ or M10 to M32. Each bolt runs about $20, so you may want to save them for a special occasion. They’re available direct from Stress Indicators, Inc., or from McMaster-Carr under the description “tension indicating screws.”