Steel Adapter, 9/16-18 Male SAE O-Ring Boss (Straight Thread O-Ring) To 3/8-18 Male NPT, Straight

Alternate Part Numbers Alternate Part Number 6401-06-06, Alternate Part Number C1EK74, Alternate Part Number MI-00318450, Alternate Part Number MINO-00028F65040	Brand Brennan Industries Inc	Brand Brennan Industries	Pack Size 1.00	UOM EA	L 1.30	Supplier Part Number 6401-06-06-O	Thread 1 9/16-18	Thread 2 3/8-18	Thread Sealant No	Product Weight 0.09 lbs

Product Questions & Answers

Will this adapter work for connecting a 9/16-18 male SAE O-ring to a 3/8-18 male NPT?

Question by: Brenda W on Jan 27, 2026, 10:13 AM

Yes, that's exactly what it's designed for. It connects a 9/16-18 male SAE O-Ring Boss (Straight Thread O-Ring) to a 3/8-18 male NPT thread.

Answer by: Customer Support on Jan 28, 2026, 8:24 PM

Model Number	Thread 1	Thread 2	L
6401-08-06-O	3/4-16	3/8-18	1.36
6401-08-08-O	3/4-16	1/2-14	1.55
6401-08-12-O	3/4-16	3/4-14	1.59
6401-10-06-O	7/8-14	3/8-18	1.56
6401-10-08-O	7/8-14	1/2-14	1.69
6401-12-08-O	1-1/16-12	1/2-14	1.84
6401-12-12-O	1-1/16-12	3/4-14	1.73
6401-04-02-O	7/16-20	1/8-27	1.07
6401-06-02-O	9/16-18	1/8-27	1.11
6401-06-04-O	9/16-18	1/4-18	1.29
6401-06-06-O	9/16-18	3/8-18	1.3
6401-06-08-O	9/16-18	1/2-14	1.39
6401-08-04-O	3/4-16	1/4-18	1.24
6401-10-12-O	7/8-14	3/4-14	1.77
6401-16-16-O	1-5/16-12	1-11-1/2	1.9
6401-20-20-O	1-5/8-12	1-1/4-11-1/2	2.17