During some winter downtime between snowstorms, I started to do some bike builds and upgrades, and I was doing lot’s of part swapping, re-installs and tweaks. A great deal of this work involved using my home shop tools, and I was really enjoying using the CDI Preset Torque Limiting T-Handle. This clever little tool uses a built in cam-over torque limiting clutch, to prevent you from applying too much torque to fasteners, which reduces damage to components and frames, and allows tightening to exact manufacturer specifications. The T-Handle’s are factory calibrated, and come in three color coded torque ranges, 4Nm (yellow), 5Nm (orange), and 6Nm (white), and retail for $30 each. They are made by CDI Torque Products, which is a sub-company of the Snap-on tool conglomerate.
When tightening a fastener to a component using the CDI T-Handle, it will click when it reaches the specific torque (4, 5 or 6Nm), and any further application of force does nothing other than cause more clicking noises, as the torque limiter prevents any additional torque application. When using a normal torque wrench the user needs to be careful with the acceleration and force being applied to the lever arm, as well not continuing once the specified torque is reached, all of which can cause over tightening issues. The CDI Preset Torque Limiting T-Handle takes the guess work out of applying too much or too little torque, and in low-torque applications, such as the assembly and adjustment of stems, handlebars, brakes, seatposts, etc., it allows precise and accurate tightening.
A torque wrench is a tool used for precise application of a specific torque to a fastener (bolt, nut, screw, etc.), to achieve the proper clamping force. It was invented by Conrad Bahr in 1918 while working for the New York City Water Department, to prevent over-tightening of bolts on water mains and steam pipes.
An interesting factoid is that only 10% of the torque applied to a fastener is for the clamping force, while the remaining portion is to overcome friction; 50% for friction underneath the fastener head and 40% for friction from the thread’s engagement. Other factors that are involved, are lubricants on the threads, fastener material, thread finish, etc.
Torque is the twisting or wrenching effect, or moment, exerted by a force acting at a distance on a body, equal to the force multiplied by the perpendicular distance between the line of action of the force, and the center of rotation at which it is exerted. The symbol for torque is the Greek letter τ.
τ = r x F
- r is the length of the moment or lever arm to the pivot point (aka the fastener)
- F is the force vector applied to the lever arm
- for example – 6Nm equates to a 6 Newton force applied to a 1 meter lever arm
- units are expressed in
- in. ozs. = inch ounces
- ft. lbs. = foot pounds
- Nm = Newton meter
- cNm = Centi Newton meter