Bill, You obviously misunderstood my post. Let me try again, and I'll go slow for you.
Please see the picture, and notice the barrel length of these two 1" travel dial indicators. IF you use a gauge with a shorter length of travel, the barrel will also be shorter, and when clamped into the head of the wall Thickness gauge, the probe tip will not reach the ball. There are long probe indicators available, but much more money than the standard, off the shelf gauge.
YES, BILL, I understand you don't need the 1" of travel, but you need the 1" gauge to fit the rest of the fixture.:banghead::banghead::banghead: