In the absence of any flow direction arrow, does it matter which way an inline fuel filter is fitted - ie should any debris be captured on the inside or outside of the actual filter?

Thanks.

I buy mine by the dozen from a power & equipment shop just down the road from me and I asked them that exact question because theirs had no flow arrows. I was told that the type of filters with no flow arrows can be installed either way. The filter media is different than the ones with flow arrows. I assume it uses a 75-150 micron screen, or something similar. They are white plastic and you cannot see the insides.

I also have a few that are clear plastic using a paper element and they do have flow arrows. But they are bigger than the white plastic filters and are sometimes hard to fit in the short length of fuel line.

Thanks Schu.

As it happens, I've just been to my local shop to buy some new ones. At first glance, they are identical to the one I've just broken  , but they now have a directional arrow - if you look hard, you can see it in the last photo in the attached link. So it seems, to answer my own question, that the filtering takes place on the outside of the mesh.

Carburation/Fuel :: Air & Fuel Filters :: Fuel Filters :: 8mm Inline Fuel Filter - Clear Polycarbonate with Micro Mesh - 21mm Diameter

Outside

The filter will work either way. I prefer having the flow come in on the visible side and flow into the filter pleats. That way you can see any contaminants.

The design of many "canister" filter elements is much stronger with the fluid flowing from the outside of the canister, through the element, and exiting to the inside.  For example, oil filters are designed this way.  

Reverse the flow and the filter will still work, unless/until the element fails because the flow was reversed and the element tears or blows apart.  Not terribly likely on a "gravity feed" motorcycle fuel system as the fuel pressure is low so even if the element gets clogged, there is likely not enough pressure to cause it to fail.  

The same is not true for high pressure oil filters or high pressure fuel systems.  High pressure filters can and likely will fail if flow is reversed.