Connect Male aerator thread (M18 x 1) to Male aerator thread (M22 x 1 / 15/16"-27)
How to join M18 x 1 male and M22 x 1 male / 15/16-27, and what stops it leaking.
Needs adapter
End A
Male aerator thread (M18 x 1) (M18 x 1 male)
Seals on washer inside the aerator housing
via adapter
End B
Male aerator thread (M22 x 1 / 15/16"-27) (M22 x 1 male / 15/16-27)
Seals on washer inside the aerator housing
Adapter neededM18 male to M22 male aerator adapter
Not a direct fit. Joining Male aerator thread (M18 x 1) to Male aerator thread (M22 x 1 / 15/16"-27) needs a M18 male to M22 male aerator adapter.
The adapter to buy
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A small M18 male spout reaches a standard M22 aerator or tap connector with an M18-to-M22 adapter. Both are fine 1 mm pitch aerator threads sealing on an internal washer, so the join is clean once the washer seats.
M18 is a genuinely smaller spout thread, not just a worn M22. An M22 aerator will start crooked on it and cross-thread; use the correct step adapter.
Related connections
Male aerator thread (M18 x 1)M18 x 1 maleMale aerator thread (M22 x 1 / 15/16"-27)M22 x 1 male / 15/16-27Male aerator thread (M22 x 1 / 15/16"-27) to Garden Hose Thread (GHT / NH)adapterMale aerator thread (M22 x 1 / 15/16"-27) to 3/4" BSP parallel (G3/4 / BSPP)adapterFemale aerator thread (M24 x 1 / 55/64"-27) to Male aerator thread (M22 x 1 / 15/16"-27)adapterFemale aerator thread (M22 x 1) to Male aerator thread (M22 x 1 / 15/16"-27)adapter
Sources: Neoperl faucet aerator thread size reference · ISO 228-1 (G / BSPP parallel pipe threads)