calipers

tulkki, työntömitta, rakotulkki A device used to measure thickness between two surfaces, especially for small or precise measurements.
1902, (w), s:Heart of Darkness|Heart of Darkness, section I,

"Good, good for there," he mumbled, and then with a certain eagerness asked me whether I would let him measure my head. Rather surprised, I said Yes, when he produced a thing like calipers and got the dimensions back and front and every way, taking notes carefully.