Australian Slot Car Racers Association

they are steel

Trophy is right they are steel
But aluminum Chassis
They are usually from 6063 or 7075 Aluminum, Ace used to use what he called Matrix aluminum which supposedly came in 6" cubes and you had to have EDM'd to whatever thickness you wanted. There are more exotix Aluminum out there but are not cost effective.
In steel chassis we have used .032, .040, .050, and .063, currently GP-12 and 27 Lite used .050.

Hof Built wrote:makin some alumium chassis for g27 lite
any one know what grade of aluminum is used ?

This doesn't answer your question, but this link to SlotBlog may be of interest.