At the risk of betraying myself to the group as a hopeless neophyte
Nothing wrong with not knowing. We were all born neophytes, and I hope that there's always something for me to be a neophyte at. A boom bail is a metal strap in a U or V shape whose ends are attached to the sides of the boom (through-bolt, drill/tap/machine screw/Pop-rivet -- you name it). The idea is that something is attached to it -- probably the mainsheet block or the boom vang. In other words it's just a convenient way to attach a line to the boom. If I remember correctly the M-15 boom has a cast aluminum fitting at the end with a hole in it for attaching the mainsheet block, so you would only need one for attaching a boom vang. Just in case: A vang is a line that runs between the base of the mast and somewhere along the boom whose function is to pull the boom down -- keeps the sail flatter when the mainsheet is out. Giles Morris Arlington VA Montgomery 15 "Umiaq" Vancouver 25 "Dolphin" Miscellaneous small craft