Common place in Japan, but sometimes difficult in the USA to source. This JDM 1/8PT (or as better known in the USA 1/8 BSP British Standard Pipe (or BSPT) are common thread sizes for many Japanese makes, including GReddy. This is common for sensors, oil cooler adapters, oil lines, water lines and vacuum lines.
(*this is NOT the same as 1/8NPT, which is more common in the USA)

GReddy Optional Hose Union Fittings

Size	Fig.	Specification	P/N	Remarks
8φ Bypass Tube	1		11900630	Machined aluminum
10φ Bypass Tube	2		11900631	Machined aluminum
16φ Bypass Tube	3		11900632	Machined aluminum
19φ Bypass Tube	4		11900633	Machined aluminum
5φ-5φ	5		11900640	Brass Cr plating
5φ-6φ	6		11900644	Brass Cr plating
5φ-8φ	7		11900641	Brass Cr plating
6φ-8φ	8		11900649	Brass Cr plating
10φ-14φ	9		11900634	Brass Cr plating
19φ-22φ	10		11900635	Machined aluminum
5φ-1/8BSPT	11	(JDM 1/8PT)	see 11900645	Brass Cr plating
6φ-1/8BSPT	12	(JDM 1/8PT)	see 11900648	Brass Cr plating
8φ-1/8BSPT	13	(JDM 1/8PT)	see 11900651	Brass Cr plating
10φ-1/8BSPT	14	(JDM 1/8PT)	see 11900653	Brass Cr plating
12.5φ-3/8BSPT	15	(JDM 3/8PT)	11900636	Brass Cr plating
5φ-1/8BSPP	16	(JDM 1/8PF) for air pressure hoses	11900637	Brass Cr plating
6φ-1/8BSPP	17	(JDM 1/8PF) for air pressure hoses	11900638	Brass Cr plating

6φ Hose Plug	A	Male Hose Plug	11900602	Brass Cr plating
8φ Hose Plug	B	Male Hose Plug	11900600	Brass Cr plating
10φ Hose Plug	C	Male Hose Plug	11900601	Brass Cr plating

EXHAUST / AIR INTAKE

GReddy - Hose Union Fitting(s) - M5-M19

GReddy - Airinx Hose Union Fitting(s) - M5-M18