Hi Wim, Checking has more to do with tail length, contour, roughing and the backcheck leather, height and angle than regulation. Hammers: Tail min. 3/4" from underside of shank Contour, radius 1/2 the shank length, center to center Roughed with 80 grit paper Backchecks: Nice unworn, undry leather Height set to 1/8" above shank at rest and 1/16" below tail at drop. Angle set so hammer cannot be tapped past check but can be driven deeper with firmer taps, about 68 degrees from verticle. Make sure keys do not chuck. Springs should not be overly strong. Try new leather. Others may have other suggestions. Newton
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