Copied from Practical Sailor (https://www.practical-sailor.com/sails-rigging-deckgear/harken-boasts-best-overall-quality-among-backstay-adjusters)
As with virtually all Harken gear, the Harken backstay adjuster is a quality piece of work.
The 1/2″ pin models have fold-down handles. Because of the fine threads, you'll be turning these handles about 20 times per inch of linear adjustment. That's a lot of turning. The handles stay folded down and store in the up position with good springs that eliminate any annoying rattles.
The Harkens have O-rings at the top to keep water out of the sealed worm tube. The rod that extends is clean.
Made largely of solid stainless and chromed bronze-with bronze worm gears, bronze thread drives and greased bearings on moving parts-the Harkens are heavy equipment.