These drive shaft guards made by boneheadrc for the HPI baja brands are made from durable plastic, they will fit stock length plastic arms of any brand.
 
The idea of these is to stop all crap from mud, sticks, stones and grass getting caught up in your boots and ripping them costing you time and money.
 
They also stop your dog bones from getting wrapped up in grass, putting strain on your drive in turn this puts more strain on your drive.
 
See the picture this is what happens when you don't run guards, yes they get wrap in grass resulting in more wear not only the cups and pins but also the gears and clutch have a hard time.

Just pre drill the arm 1.5mm diameter in the arms for fitting self tapping screw supplied.
Note engraving as been replaced for 2 BoneHead stickers, these are water, oil, petrol resistance so the colour never fades or gets washed out.