Serial connections can be confusing and are even more so when you try to connect devices to the older Apple Macintosh computers. However, you can trust Monoprice to have the cables you need for almost any situation!
The Macintosh Plus (Mac+) used an 8-pin mini-DIN connector for it's serial output, which used the balanced RS-422 interface, instead of the more common RS-232. However, with proper wiring, this can be connected to standard RS-232 peripherals.
This cable connects the Mac+ to a standard RS-232 external modem with a DB-25 connector. It has molded plugs and the DB-25 end has thumbscrews to secure it to the modem.