Get your guitar in tune! These guitar machine heads are for steel-string acoustic guitar. 6 collars are included with each set (a collar is a round silver piece which is placed over the rod of the machine head for a neater look and better stability). Each machine head has a cap to cover the open tuning gear, each cap has 2 holes for skrews. 6 skrews are included for fitting. These machine heads are meant to be fitted 3 per side.