Are you sometimes haunted by thoughts of being catapulted into the air or rammed to the ground on one of your favorite rides at the theme park?

Your safety is determined, in many cases, by applying the proper torque and tension to various fasteners on the ride. If the maintenance staff has applied the right amount of tightening torque and if there is sufficient tension on the fasteners (nuts and bolts) that keep the roller coaster securely on its tracks, you can allay your fears and enjoy the thrill of the ride.

Torque is the term used to describe the amount of force required to overcome friction between the nut and the bolt. Tension is used to indicate the amount of stress to place on a bolt or fastener so that it remains within its elastic limit (yes, threads in metal bolts and nuts have minute, unobservable elastic qualities). When both are applied within the specifications, there is enough clamping force to carry the load.

The question asked sometimes is: How much torque is required to tighten this fastener? Although this question requires some mathematical calculations, it is estimated that 50 percent of tightening torque is needed to overcome friction between the nut or the bolt turning against the joint surface. Another 40 percent on average is used to overcome friction between the mating threads, and the remaining 10 percent develops useful tension in the bolt.

For a bolt to tighten parts properly together -- like on that Ferris wheel you love to ride on -- it must be under correct tension and must be stretched to accurate amounts. Over-tightening can cause a fastener to deform, distorting the threads, and, in fact, can become loose as the part goes through stress -- just the opposite effect you want!

Another nightmare is under-tightening. It can cause a fastener to loosen and actually come apart. This can cause a shearing force to develop between the mating parts -- nut and bolt -- which may cut the fastener in two.

Carl Kovich knows about torque and tension, and most everything else having to do with nuts, bolts and screws. His company, Bayou City Bolt in Houston, Texas, is one of the oldest fastener supply companies on the Gulf coast of the United States.

Kovich cautions that proper fastening practices is the best way to ensure safety and proper operation of mechanisms.

"Be sure the wrench fits snugly on the nut or the bolt head," he said. "Clean all threads but lubricate only at the manufacturer's recommendation. Never hammer a regular wrench. Never use a bar or pipe to increase leverage on a wrench. Do not use makeshift tools such a vise grips and pliers to tighten fasteners. And always pull on a wrench with a smooth, even motion."

This is the kind of advice Kovich's customers get when they purchase supplies from his company. Over the past 40 years, Bayou City Bolt stocked inventory in its nine warehouses from as small as eyeglass screws t as large as eyebolts used to anchor ships.

"While it is an inventory headache, we still have some fasteners that are more than 25 years old. But, when a customer calls looking for a screw or bolt to repair a very old, no-longer, manufactured machine, we realize how important it was to inventory those parts for all of these years," he said. "We have to stock the sizes, head styles and threadings required by the industries of the 21st century."

Opened in 1962 by Louis Palombi and still privately owned, Bayou City Bolt provides fasteners for a diverse clientele, from computer and electronics to construction and heavy machinery manufacturing industry, to oil, gas and maritime industries.

For more information, visit www.bayoucitybolt.com.

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