The “NeckCaps” file (openscad) allows to design your own necks/caps for your DIY projects.
Examples are given for three widespread closures of PET bottles:
• 28 mm pco 1810 (pitch 3.18 mm, old std) – (used for water/soda bottles)
• 28 mm pco 1881 (pitch 2.7 mm, new std) – (used for water/soda bottles)
• 38 mm 3 start – (used for fruit juice bottles, flat beverages)
So you can make your own containers/bottles with these necks and use regular HDPE caps from your water/soda bottles.
You can use the caps in many different DIY bottle projects such as: bottle connectors, pet water dispensers , plant watering . . .