critical dimensions for a replacement upright & Yokes is the
diameter of the bell bowl and the inside gap of the yoke. The inside
gap is the distance across the yoke, excluding the end pins that rest in
the open saddles of the upright.
If the bell is in the
way and prevents an accurate measurement of the inside gap, we suggest a
caliper to measure the inside gap without having to remove the bell
bowl. A caliper can be made from two sticks to place one tip on one
side of the yoke and another tip on the opposite side. Then grip the
sticks firmly and place them on a ruler or measuring tape to determine
the dimension, within 1/8th of an inch.