15ml Essential oil bottle has an 18mm closure neck. Volume specified is the nominal manufacturers claim as with most bottles a fill right up to the neck is a small percentage more than nominal.
This cap has a tamper - evident skirt and is flared at the side.
its assembled as one piece - you screw in the whole cap and its done - sealed!
the white dripolator insert has one hole in the middle.
Height for label 37mm, height with cap 65mm, diameter 26mm