Aero 300

The centres come as ‘Standard’ or locking, the price differential is small so we recommend the lockable version.

We suggest you adjust the cap to have a light easy action, if it is hard to open it is too tight – fingertip pressure is fine – the cap is nicely engineered – it is not American or a trial of strength!

If you have access to both sides of the assembly, i.e. before you fit the flange, close the cap up and just check that the retaining saddle is firmly engaged, not free to rotate.

So long as the seal is held against the flange it will be sealed, no need to crush the seal to a wafer.



Try to keep the cap clean, dust, especially sanding dust, seems to migrate down the centre pin, sets like concrete and disrupts the O ring seal- if there is a leak from the centre, try a strip and clean. Lubricate lightly with eg Vaseline or silicone grease. Please protect the cap from dirt during the build process.

O rings do not last for ever, even the Viton kind we use. Maybe change them every ten years? Even every five?

The Aero 300 uses Viton O rings 45 x 3.5mm and 5 x 1.5.

Your supplier can offer an overhaul kit pretty cheap with new nylocks, seals and an E clip for the lock. Always insert the key in the lock before you dismantle- there are 5 lock wafers and 5 tiny springs just waiting to spray them around the room.

The standard flange is supplied with Metric socket screws- looks super, unless you used imperial hex keys which do work, but leave the part looking like a dogs dinner….

The special flanges are:-

Glass-in to build into a composite skin.

The flange is machined down on a taper so it is always below the curved wing surface.

We suggest drilling lots of large holes in the flange so it bonds into the composite structure, and avoids adhesive delamination around the filler hole.


G/S built for the Glastar but now widely used to thread into a tank and screw down ˜flush˜ to the skin.Ideal for wooden aeroplanes avoiding recesses and doors eg for the Falco.

The 2 5/16′ thread conveniently fits a 2.25’ hose, and the flange can be retained to a skin by our special back nut, still leaving room for a hose.


Cirrus A low profile threaded flange is designed for Cirrus so as to enable the cap to be fitted after the wing is painted- avoiding damage, dirt, masking, filling and other nuisances.

Cirrus use our threaded bush NC034 which also accepts the Glastar flange above which we suggest is better riveted than welded- welding always distorts threads …

The same part can be glued in place – just a wipe of “pro-seal” – place in position, and the job is done.


Vans offer our 300 cap in a special flange machined to fit the wing profile, and rivet inside the tank. (This means our ‘Aero’ cap can only be fitted when the builder makes the tank. Fastbuild wings come with the Vans cap fitted.) 

They call ours the “Luxury” version, but my view is that this is a very worthwhile change. 

We offer a retrofit assembly that will go into Vans standard flange, available from Vans and ‘Spruce, Vans are using out lightweight ‘Sprl cap’ in the RV 14, one hopes they will standardise on our cap one day.

Vans Catalogue

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