Low-friction Carbo AirBlocks® are lightweight. strong. reliable—and affordable. Companions to the popular Harken® Black Magic® line. these small. compact blocks have very high working loads for safe. easy trimming. The 40 mm fiddle is an excellent choice for 3:1 and 4:1 tackles on dinghy vangs and mainsheets. as well as for controls such as cunninghams and internal boom outhauls on larger boats.