What [MENTION=392125]79pmooney[/MENTION] is referring to are old style road dropouts, which face forward and slope down slightly to match the angle of the rear brake mounting bolt, so the brake pads don’t need to be readjusted when the wheel is moved in the dropout. They were replaced in the 1980s with vertical dropouts, because there was no need with a derailleur to move the wheel to adjust chain tension and vertical dropouts secured the wheel much better. You will still see these semi-horizontal dropouts on some multi-purpose frames the are used both as multi-speed and single speed. My Salsa Casseroll is set up that way. Compared to track dropouts, they also have the advantage of making wheel removal much easier with a full fender. So, if you pay to have a custom built frame, then you might as well have the builder use them instead of track dropouts if you intend on having a rear brake and/or a rear fender. Otherwise, track dropouts work just as well.