Thread identification
AC Line Fittings (Tube-O, Spring Lock, Block)
Automotive and equipment AC lines use their own fitting families — tube-O with captured O-rings, spring-lock couplings, and block-style manifold pads — none of which interchange with hydraulic fittings, even where threads look familiar.
Identify it
Four checks at the bench.
- 01
Identify the style: threaded tube-O nut, spring-lock collar, or bolted block pad
- 02
Note the tube OD in sixteenths (#6 = 3/8", #8 = 1/2", #10 = 5/8", #12 = 3/4")
- 03
Check for the green HNBR O-rings AC systems require
- 04
Barrier hose only — hydraulic hose is never acceptable for refrigerant
Don't confuse it with…
- Hydraulic JIC 37° looks similar to some AC flare ends but seals differently and isn't refrigerant-rated
- Black NBR O-rings will fail in refrigerant service — AC uses HNBR (usually green)
Reference
Size chart.
| Size | Thread |
|---|---|
| #6 (3/8" tube) | suction/liquid lines |
| #8 (1/2" tube) | discharge lines |
| #10 (5/8" tube) | suction lines |
| #12 (3/4" tube) | suction lines |
Unsure even after the checks? Bring the fitting to the counter — gauging an unknown thread takes us about a minute. (817) 589-7101.
AC Line Fittings (Tube-O, Spring Lock, Block) — FAQs
Can you crimp my AC line with hydraulic fittings?
No — and neither should anyone. AC lines need barrier hose and AC-specific fittings and ferrules; that's exactly what our AC line bench builds every day.
What size is my AC line?
AC sizes follow tube OD in sixteenths: #6 is 3/8", #8 is 1/2", #10 is 5/8", #12 is 3/4". Bring the line and we'll match ends and length.