This plug is used to close off the end of a pipe.It is similar to a cap but it fits inside the fitting it is mated to.In a threaded iron pipe plumbing system, plugs have male threads.

NPS	A(Length)	F(Width Flat)	Hex Head	Square Head	Round Head
1/8″	10	11	6	6	35
1/4″	11	16	6	6	41
3/8″	13	18	8	8	41
1/2″	14	22	8	10	44
3/4″	16	27	10	11	44
1″	19	36	10	13	51
1-1/4″	21	46	14	14	51
1-1/2″	21	50	16	16	51
2″	22	65	18	18	64
2-1/2″	27	75	19	19	70
3″	28	90	21	21	70
4″	32	115	25	25	76