Say you are rebuilding a 1964 AC Cobra classic car, and you are lucky enough to have started with an original Shelby chassis. Then, say you had a custom hand-beaten aluminum body, a rebuilt 427 V8 engine and the finest leather interior known to man.

What kind of axle system are you going to use a generic design with low-grade materials, or an axle system using the most advanced technologies and the lightest grade materials? This may seem an odd question with an obvious answer.

In the booming inline skate market, a similar scenario is taking place. Bob Aamadt, founder of axle-maker In-Line Edge of Newbury Park, Calif., said, "If you buy the best wheels, chassis and bearings, you owe it to yourself to buy the best axles. Axle systems are not just axle systems. Dare to compare!"

I found 21 companies that have "hop-up kits" available at a store near you. A hop-up kit is a package containing bolts, spacers and sometimes washers that, when assembled, create the axle upon which the wheels and wheel bearings rotate. The spacer separates the two bearings of a wheel and is either threaded on both ends, or hollow (a free-floating spacer).

The threaded spacers have two bolts which screw into either side of the spacer, securing it to the chassis. Free-floating spacers typically have one female bolt which runs through the spacer, and a screw which threads into the female bolt, securing it to the chassis. Originally, spacers were made of plastic, but now they can be manufactured in various grades of aluminum, brass, zinc-plated steel and even stainless steel.

What's the difference? Actually, the difference is quite significant. Plastic spacers become fatigued and break. They compress when tightened, which skews the bearing's alignment, creating an unstable axle and, thus, a wobbly ride.

Aluminum spacers usually come in one of three series of aircraft-grade aluminum: 2,000, 6,000 and 7,000 (the latter being the highest grade). They are light and much stronger than plastic. There is no compression problem and therefore the axle is stiff and the ride is smooth.

Brass spacers are even stronger than aluminum but are a bit heavier. If you skate hard and/or are heavy, you may have trouble with warping or bending the aluminum spacers, in which case, you should use brass. Steel spacers are even stronger still. But they, too, are also heavier. They are usually for the extreme or aggressive skater who can break even the brass spacers. That's not to say some hockey players won't benefit from them as well.

Many variations and specifications are evident from one company's kit to another. The kits themselves are being manufactured for specific areas of inline skating (such as aggressive skating, speed skating or hockey), as well as for specific age groups (especially for kids). There are kits designed to upgrade low-end skates and kids skates (typically found in K-Mart or Target stores), which is a great idea for kids whose abilities have outgrown their skates.

Additionally, some chassis manufacturers custom make their axle kits for their own frames. They may have a completely unique construct, such as Labeda's triangular axle head, or maybe they just don't want to enter the hop-up kit market. Whatever the reason, the following companies only provide axle kits for their own chassis: Canstar, Charger, Labeda, Rike, U.S. Hockey Research, V-Form and V-Burn.

Basically, no matter what your size, weight, age, ability or style, there is a hop-up kit made just for you.

The following companies have hop-up kits on the market that will fit most brands of skates:

A.K.S.

BULLZEYE

CONCEPT DESIGNS