Rubber style with two attachments for vinyl blow off hoses (3/8 or 1/2''). For use with our 3, 5, 6, or 6.5 gallon glass carboys with smooth necks. Can also be used on 5 and 6 gallon plastic carboys,,TIP: Carboy hoods are exceptionally useful for blowoff tubes. Just add 3' of 1/2" racking tubing into a bucket of water as your airlock.