They're most likely -6.
Here's a tech article I wrote for my own site. Sorry the table comes out a little crappy. I have no other way to post it here. You'll have to count cells.
The AN system is often a source of confusion. It however is, a real handy and easy to understand system once you understand how, and especially why it's used the way it is.
The AN sizes are shown as dash #, for example -6. The numeral represents a fraction of 16. So -6 stands for 6/16 = 3/8.
What this means is, that a -6 AN sized piece of hardware is compatible with a 3/8 OD hard line. This makes figuring out what combination of hard line, flare size, tube (b-) nuts & sleeves and adapters you will need to mate it to a flexible line using hose ends.
The dash size does NOT mean your flexible line has an ID represented by the dash size. What it does mean is, that the hose and hose end have an ID comparable to the ID of a 3/8 OD hard line.
So, if for example you want to plumb a system starting out with a 3/8 OD sized hard line, you will need -6 sized components.
You will need one -6 flare (b-) nut and one -6 flare sleeve and a 3/8 sized 37 degree (double) flare to create your hard line coupling. This will then mate to a -6 sized male adapter or hose end (provided you have a male ended hose end). In case you have an ordinary female ended hose end, you will need a -6 flare union to hook the hard line to your -6 sized hose with the -6 hose end.
Some sizes are uncommon in automotive applications, an example is the 5/16 or -5 size. 5/16 is commonly used for fuel lines and automatic transmission cooler lines. The problem is, a -5 hose and hose end is impossible to find. What you need is a -5 flare (b-) nut and sleeve and a -5 to -6 flare union. Aeroquip sells these.
Here's a stainless tube, single flared for a 37 degree flare (this is seamless aircraft quality tubing, a double flare is only needed on non seamless tubing) with (from left to right) a flare (b-) nut, a flare sleeve and on the right an an adapter fitting (with in this case some custom fabbed breather gizmo)
For low pressure applications you can also get away with using a tubing or hard line adapter. These are usually (the popular automotive ones) pretty anodized aluminium fittings with a brass ferrule. Because of this they don't bite the steel tubing well enough to be used in high pressure applications. An automatic transmission cooler line however can be easily plumbed with them, and the neat thing is, they come in male and female, so if you want to use hose ends make sure you use the male type.
Some manufacturers (like Russell) have a tech paper on their site instructing that the fractional sizes directly represent the hose sizes. This is wrong (and I have no idea why they print that)
AN Size - 2 - 3 - 4 - 5 - 6 - 8 - 10 - 12 - 16 - 20 - 24 - 28 - 32
Tube OD 1/8" 3/16" 1/4" 5/16" 3/8" 1/2" 5/8" 3/4" 1" 1-1/4" 1-1/2" 1-3/4" 2"
SAE Thread Size 5/16-24 3/8-24 7/16-20 1/2-20 9/16-18 3/4-16 7/8-14 1-1/16-12 1-5/16-12 1-5/8-12 1-7/8-12 2-1/4-12 2-1/2-12
B-Nut Size ... ... 9/16" ... 11/16" 7/8" 1" 1-1/4" 1-1/2" 2"
Pipe Thread Size (NPS) 1/8-27 1/4-18 3/8-18 1/2-14 3/4-14
Here's the table shown on the Russell and Edelbrock site. This is wrong!
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