Measuring a mouthpiece - Johan Jonker 0.1 mm. M. This is easy to measure. Take care to measure the length along the line of the flat part of the table. P_table can be measured with a bevel. Place the mouthpiece with the bottom of the shank against the arm of a bevel. Hold the other arm along the table and fix the screw on the corner. A suitable bevel can be easily made: