5.5mm x 2.1mm Standard Center Negative
This is the most common plug type found on Boss, most Ibanez, most Dunlop, MXR (new Dunlop-era), Line 6 ToneCore (not digital modelers), current Voodoo Lab effects, Prescription, most Fulltone, new DOD, Danelectro, Maxon, Morley, Guyatone, and many more.

18"/46cm long 

24"/61cm long

36"/92cm long