AirBlocks have a lightweight design and a unique patented bearing system which uses stainless steel balls in a captive, grooved race. Very high working loads in an extremely lightweight block, with the best strength-to-weight ratios around.
Part of the standard XD rig if you have a Laser with it. If you don't it is worth the money to get the little micro blocks for the outhaul and make up your own - a great adjustment to have in variable winds. 1 block with becket, 4 plain blocks. Of course that leaves the downhaul with no cleat - I just tie it off.