Bellows Card Depth in Instrument Construction & Repair Posted September 5, 2018 The measurement I have observed on jeffries cards was 1" and 1/8th" or something near 28mm. The benefits of folds deeper than 1" which was standard on Wheatstone and Lachenal instruments is something which experts seem to disagree on. The argument against is: the bellows are able to extend further but the deeper folds mean there is a smaller volume of air inside. In such a case you would have a bellows that comes out further but does not actually have any more air inside. But others believe that the deeper folds do give you more air. I have been told conflicting things on the subject. If anyone could mathematically or otherwise calculate weather a 6" wide 7 fold bellows with 1" deep folds has more or less air inside than a 6"wide bellows with 1" and 1/8th" bellows I would be very interested to hear what the answer would be. I was thinking about building a deep fold jig at one point but am unsure if I should bother. alternatively: build one of each and fill them both with water and see which holds more ?