Measuring for spares that actually fit

Before anything: write down what you already own

Every check below starts from a model number. Find it on the stuff sack label, on the stove body, on the filter housing, and write the whole string down — not the range name, the model. Cartridges, splints and pole sets are listed by the things they fit, and visual similarity between brands means nothing at a seal.

Take a photograph of each label while you are at it. Labels fade, and the one on the flysheet is the one you will want in the rain.

1. Pole diameter, across the tube, with callipers

This is the first measurement because it is the one with no tolerance for guessing.

Replacement pole sections come in a narrow band of outer diameters — 7.9, 8.5, 9.0, 9.5 and 11 mm are the sizes you meet — and the ferrule that joins two sections is machined to one of them. Measure across the tube, not across the ferrule, because the ferrule is deliberately wider.

The same figure decides the pole splint in a repair kit. A splint is a short sleeve that has to slide over the pole’s outer diameter, so a kit built around 8.5 mm does nothing at all for an 11 mm pole. Measure now, not after it snaps in the dark.

2. Section length and total assembled length

Two further pole numbers follow, in order.

Section length is usually somewhere between 40 and 65 cm, and it sets both the folded size and how many sections a set needs. Total assembled length is what actually has to match the sleeve or clip run on your tent, and it is the one people forget to check because the diameter felt like the hard part.

While the pole is out, look at the shock cord: note its diameter, and whether it is slack. A tired cord is the usual reason an old pole will not stand up, and a replacement length is cheaper than a pole set.

Material is not a measurement but it is worth recording. 7075 aluminium bends before it breaks and can often be straightened; fibreglass is cheaper and splinters; carbon is lightest and least forgiving.

3. The stove: read the valve wording, not the picture

Nothing in camp kit fails on compatibility as bluntly as a gas canister — the wrong valve simply will not go on.

Three systems share the shelf. The EN 417 threaded canister, with its 7/16 inch UNEF screw valve, is what most modern backpacking stoves take, and it is resealable. The bayonet canister is a different fitting entirely, common on cartridge-style stoves. The pierceable canister has no valve at all and cannot be removed until it is empty.

Read the wording in the stove manual and match it exactly. Then take two more numbers before ordering: the net gas weight, commonly 100, 230 and 450 g, which is the gas rather than the steel shell you also carry, and the canister diameter and height, which decide whether it nests inside your pot and how stable the stove sits on top of it. Follow the canister’s own handling instructions in all cases.

4. The filter: the housing decides the cartridge

A cartridge is a spare part, so the first question is not performance but which housing it fits.

Look up the exact filter model and read the maker’s list of compatible housings. Where a cartridge screws onto a bottle or a pouch, the fitting is usually a 28 mm threaded neck, and the maker names the standard. Only once the fit is settled do the published figures matter: the pore rating in microns — hollow-fibre cartridges are commonly stated at 0.1 or 0.2 µm — the rated capacity in litres, and the flow rate, which is quoted for a new, clean element.

Those are manufacturer figures describing the membrane. What the cartridge is intended for, how it must be backflushed and stored, and anything about whether water is safe to drink are set by the maker’s instructions and by local authorities, not by a dimension.

5. Bottle mouth: 63 mm or 42 mm

A bottle is a hub for other kit, and the specification that decides what attaches to it is mouth diameter.

The 63 mm wide mouth is the de facto standard that filters, gravity bags and insulated sleeves are built around. A narrow 42 mm mouth drinks more cleanly on the move and accepts far less. The two families do not interchange, adapters exist and leak more often than the bottle does, and if you already own a filter the sensible move is to buy the bottle whose thread it fits.

The same logic applies to a hydration bladder: check the hose internal diameter, whether there is a quick-disconnect at the reservoir, and whether the shut-off on the bite valve is the part that has failed before you replace the whole reservoir.

6. The coating, before you buy any tape

This one is read rather than measured, and it catches more people than the pole diameter does.

Find the flysheet label. Silicone-coated fabric — silnylon and silpoly — rejects ordinary adhesive tape and needs a silicone-specific repair tape or sealant. Polyurethane-coated flysheets take conventional self-adhesive repair patches. Makers state which coating their tape is for, and the two are not interchangeable: silicone tape on a PU fly and PU tape on a silnylon fly both peel off, usually in the rain.

The same question governs the seam sealant in the repair kit, so buy the two together and buy them for the coating you actually own.

7. And where the rule is subtraction: the footprint

Worth restating here because it is the one compatibility that runs backwards. A footprint has to be smaller than the tent floor, not larger. Take the floor dimensions from the tent specification and subtract 3 to 5 cm on every edge. A sheet that sticks out past the flysheet funnels rain to exactly where you are sleeping.

Keep the numbers with the kit

Write the pole outer diameter, the section length, the canister valve type, the filter model and the flysheet coating on a card, and put the card in the repair kit. It weighs nothing, it lives where you will need it, and it turns a hunt through old listings into a thirty-second order.