18mm neck - these bottles are supplied without caps.
FILLED TO THE BRIM THESE WILL HOLD 18ML
Caps for these bottles are located in the Dripolators section.They have 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.
If you wish to choose an option for a cap please choose 18410 dripolator cap, or 18410 black screw cap or 18410 spray, or 18410 pump