Linked multiple individual plastic cases, that clip-on onto a 1/2 x 1/8" single speed type bicycle chain.
Mounts directly to the chain and does not attach to the frame. 
Can be used when alternative frame mounted chainguards are not an option. 
(Not suitable for derailleur gears or pulley type chain systems)
Specification 
Length: 120 links
Material: plastic 
Colour: Black 
Weight: 125g