This is a plug often used in audio-related Products. It is also referred to as a standard phone plug, stereo cable, 1/4-inch size, 6.3 mm size, or a balanced or unbalanced cable.
TS phone, TRS phone

PL01A(TS (Mono))
A (External shape):2.5mm
B (inner diameter):10-12mm
PL01B(TS (Mono))
A (External shape):3.5mm
B (inner diameter):10-12mm
PL02A(TRS (Stereo))
A (External shape):2.5mm
B (inner diameter):10-15mm
PL02B(TRS (Stereo))
A (External shape):3.5mm
B (inner diameter):10-15mm