They will fit most makes of greenhouse new or old if rebuilding an older greenhouse with imperial bolts and nuts these will be fine but you will not be able to mix the two threads. Square Head Bolts are used during the construction of the aluminium greenhouse the 10mm square head will fit into the channel on the underside of the glazing bar so you can slid into the position required because of the larger head size they will add more strength to the build than the cropped bolts.
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