A cable gland is unsuitable, they are huge and designed to seal hermetically. Use a strain-relief grommet. Sometime like this: https://www.rapidonline.com/Anixter-3001150-Strain-Relief-Bush-6-4-7-4mm-Cable-04-0262?IncVat=1&pdg=pla-339154412538:kwd-339154412538:cmp-757438067:adg-44804851896:crv-207912323492:pid-04-0262:dev-c&gclid=CjwKCAjww6XXBRByEiwAM-ZUIMoUfMQxzKTi0ZLKIAyHH6oE3CJVSPf3dutB8xNcmfMDo7Y8z_atNhoCtN0QAvD_BwE