Hydraulic fitting oring replacement size

[ponytug]

Now sure what the problem is exactly. How else will he figure out the size if the doesn't pull an o-ring out? I doubt anyone here will know the size of the o-ring anyway.

Micrometer / "slide rule" (UK) would work; diameter and cross-section, but one has to allow a bit for compression and distortion of the existing o-ring.

@BC Dave yes, backing rings tend to be flat, hard, and cut to allow them to be inserted against the o-ring. They are usually an oil resistant plastic that will function in the desired temperature range.

Here, I keep a stock of o-rings in a variety of sizes, metric/SAE, and materials. I find it usually cheaper to stock a selection than buy a single size. Memorably, I bought an assortment of 100 fluorinated o-rings for less than five of one size. Parts pricing can be odd in my experience.

All the best,

Peter