The design of our jacks was originally inspired by Ruckers jacks, particularly where the dimensions of the tongues are concerned, and to some extent the thickness of the bodies.
Tongues are currently cut from very nice straight and quarter sawn hornbeam, to maximise the strength at the plectrum slot (slab sawn tongues are 4x weaker than quarter sawn, and hence 4x more prone to splitting). They are 31 mm long by 4.2 mm wide and 2.8 mm thick, fully shaped in profile and aspect. We no longer use a cut across the back of the plectrum slot, as this just weakens the tongue at the slot. The aim is to maximise the strength of the tongue at the plectrum slot, and lighten it as far as possible elsewhere. There is a 6 degree upward slope on the plectrum slot.
Similarly the jack body we try to make quarter sawn — as did Ruckers — giving a 4x stronger damper slot, and a more stable jack. Rock maple has served as the material for recent years. Wild Service, pear, holly, and beech are other possible materials.
Tapered jacks
12.8 mm x 3.5 mm at their top, and 11.8 mm x 3.0 mm at their bottom. The tongue is to the right, as looking from the front (plectrum side).
Italian jacks
12.8 mm x 4.5 mm at their top, and 12.8 mm x 4.3 mm at their bottom. The tongue is to the right, as looking from the front (plectrum side).
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