According to the 501st requirements:-Two diameter circular are 18mm

• Interlockable parts, no need to worry about loose parts when transporting it.
• The hole for the audio jack has an opening of 3.5mm hole.
• The side hose connectors has an opening of 37mm hole
• The middle hose connector has an opening of 37mm hole
• It has 4 rectangle holes that accept nylon webbing width of 24mm.
• At the back you can see it's hollowed out, dedicated for storage such has trading cardsFor better quality printed parts, print the audio jack and male snap in resin on a resin printer. Better yet, use the real counter parts used in audio jack ports and a snap from a snap kit DIY or bought separately at a hobby shop