Design me plastic Fitness Dumbbells to be filled with water

Create and design plastic made dumbbells that can be used for personal and outdoor training. The quality must be high and sturdy as dumbbells are repeatedly being dropped, dragged, and re-racked. I propose having the opening on the top of one side that can be screwed in securely, like a petrol tank cap. The aim is for the design to be hard plastic cased which can be filled with water to provide resistance. It’s essential that the top cannot be released by accident. While in use it must be secured tightly at all times. Colours to be used are red, black and grey. I’m looking for a sleek design which can be used by individuals at home or in a commercial gym. The casing must be strong enough to be thrown around. Going up in 10kg increments. 10kg – 20kg – 30kg – 40kg -50kg – 60kg Looking for a knurling pattern to be carefully chosen. Finding the knurling depth strike the perfect balance between a grip that feels solid and a grip that feels comfortable. Looking for the grip to be a special 35mm fixed grip. Size should be replicable to a standard size dumbbell. Longevity is key importance for gym equipment. These are dumbbells you can pass on to your children’s children! These dumbbells should come with an industry best Lifetime Warranty as standard. Attached are photos and design templates to give guidelines to follow.