I lost the fittings that came with my Stainless line. I called ARB to try and figure out what size I needed, and I was told, "ARB Air Line Adapter Fitting 1/8 BSP (M) JIC-04 (M) - 2Pack ARB0740105".
In the hopes of helping someone else, this is what I found. The solenoid and bulkhead fitting are both 1/8 BSP and the fittings on the SS line are 3AN. I noticed it was not holding pressure, so I did a soap test; that's when I remembered that the original fittings included a washer; it's called a "Dowly Sealing Washer."
The only place I could find the 1/8 BSP male to 3AN male adapter fittings was at PegasusAutoRacing.com. I wish I had found them before cobbling together a 12' line and a 3' line to reach the rear axle. They could have made a custom-length hose cheaper than the two individual hoses.