Joined: Feb 2006
Posts: 647
Likes: 1,068
From: Marin County, California
Bikes: Breezer Repack 650-B, 2011 Gary Fisher Rumblefish II, Gary Fisher HiFi 29er, 1983 Ritchey Annapurna, 1994 Ritchey P-21, 1978 Breezer #2, 1975 Colnago, Ritchey P-29er
It's a Koski dropout. Invented by the Koski brothers (Don, Erik, Dave) who designed the ProCruiser and the Trailmaster bikes in the '80s.