This lens cap is for optical instrument (eg. binoculars, telescopes and spotting scopes) and accessories (eg. eyepieces, Barlow lenses).
Internal Diameter: 40mm
(Note: this is measured as internal diameter of the cap, which is equivalent to the external diameter of the lens including the lens housing).
Depth: 9mm
Material: Plastic
Note: This listing is for ONE lens cap as described above (not for a pair). The cap is made of plastic. Please measure the external diameter of the lens to make sure it's around 40mm.

Note: The size of the lens cap is measured as Internal Diameter of the cap, which is equivalent to the external diameter of the lens including lens housing (as shown in the picture above). Please allow a small difference in measurement (eg. 0.5-1mm). The plastic cap is quite rigid so it can be difficult to fit a lens which is larger or smaller than 40mm.
If a cap is slightly bigger than the external diameter of the lens housing and there is no matched cap size available for the lens, you may consider putting an adhesive cloth tape around the internal edge/rim of the cap. This can often secure the cap on the lens.