Hello Jamie,
I generally use what I come in contact with however the spiders body I have used mill and sag mill balls they are solid and made from specialized steel to handle the constant impact and wear. They are wildly use in the mining industry to crush the ore into a fine paste. They range in size from 125mm dia( 5" inch) to 25mm dia ( 1" inch), I have used all the sizes available in the making the five different size redback spiders and range in weight from 16 kg the largest to the smallest at 500gms. The legs are solid also and range from 16mm dia ( 5/8")to 3mm (1/8").I have also made lady bugs from split balls and caterpillars from the 75 mm ( 3" inch) dia balls, will post photo's.
Cheers For Now Michael.