If it's 531 straight gauge it probably uses a 26.4 seatpost like my Gazelle Champion Mondial semi-race from 1978. It is a good idea to get some proper measuring done with vernier calipers though.
@taiAta started
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If it's 531 straight gauge it probably uses a 26.4 seatpost like my Gazelle Champion Mondial semi-race from 1978. It is a good idea to get some proper measuring done with vernier calipers though.