421-06-05-BLK 3/8" NPT to 5/16" Hose Tail - Black

Speedflow SF421-06-05-BLK | 3/8" NPT to 5/16" Hose Tail | Black | 421 Series

The Speedflow SF421-06-05-BLK is a precision-machined 3/8" NPT male to 5/16" hose tail adapter in black anodised finish, part of the Speedflow 421 series NPT hose tail range. A step-down adapter connecting 3/8" NPT ported components to the smaller 5/16" (approx. 8mm) rubber or silicone push-on hose, this fitting is ideal for applications where a 3/8" NPT port needs to feed a smaller-bore hose run — such as oil pressure feeds, sensor lines, and turbo oil connections where 5/16" hose is the build standard.

Product Specifications

• Part Number: SF421-06-05-BLK
• NPT End: 3/8" NPT male
• Hose Tail: 5/16" (approx. 8mm) barb
• Finish: Black anodised
• Series: Speedflow 421 — NPT Hose Tails (Aluminium Barb Fittings)
• Compatible With: 3/8" NPT female ports and 5/16" ID rubber or silicone hose

Applications

The SF421-06-05-BLK is suited to applications where a 3/8" NPT port connects to a smaller 5/16" hose run, including:

• Oil pressure sender and gauge line connections from 3/8" NPT ported blocks and coolers
• Turbo oil feed line connections from 3/8" NPT ported components stepping down to 5/16" hose
• Coolant line connections from 3/8" NPT ported thermostat housings to smaller hose sections
• Fuel line connections from 3/8" NPT ported regulators and filters
• Any application requiring a 3/8" NPT male to 5/16" step-down hose interface

421 Series 3/8" NPT Hose Tail Range — Choosing the Right Size

The Speedflow 421 series offers three hose tail sizes for the 3/8" NPT port, covering step-down, matched, and step-up configurations:

• SF421-06-05-BLK — 5/16" hose tail: step-down for smaller hose runs (this listing)
• SF421-06-06-BLK — 3/8" hose tail: matched size for direct 3/8" hose connections
• SF421-06-08-BLK — 1/2" hose tail: step-up for maximum flow capacity

NPT Installation Note

NPT fittings use a tapered thread that seals via thread interference. Always apply appropriate thread sealant or PTFE tape to the NPT male threads during installation. Do not overtighten — NPT threads can crack cast components if over-torqued. Secure the hose tail with an appropriate hose clamp for pressurised applications.

Sold individually. Compatible with 3/8" NPT female ports and 5/16" ID rubber or silicone hose.