Nomenclature variants
A plurale tantum sense of the word "calipers" coexists in natural usage with the regular noun sense of "caliper". That is, sometimes a caliper is treated cognitively like a pair of glasses or a pair of scissors, resulting in a phrase such as "hand me those calipers" or "those calipers are mine" in reference to one unit.
Also existing colloquially but not in formal usage is referring to a vernier caliper as a "vernier" or a "pair of verniers". In imprecise colloquial usage, some speakers extend this even to dial calipers, although they involve no vernier scale.
In machine-shop usage, the term "caliper" is often used in contradistinction to "micrometer", even though outside micrometers are technically a form of caliper. In this usage, "caliper" implies only the form factor of the vernier or dial caliper (or its digital counterpart).