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A strainer insert looks like the simplest part on a bottle and is quietly one of the pickiest. It screws into the neck from inside, another lid screws onto its external thread from above, and both threads are on the same moulded wall. The perforated screen has to hold leaves and tea back while letting liquid through fast, and the whole thing has to come out of the tool with the threads intact, because threads do not forgive flash.
The part shown here is a replacement strainer insert in smoky-translucent plastic, with internal and external threads on the same skirt, a perforated screen moulded across the base, and two sliding buttons on the rim that locate it in the bottle.
Carrying internal and external threads on the same skirt is the defining constraint of this part. The internal thread accepts the fitting below; the external thread takes the lid above. Both need full form to seal and to carry the tightening torque, and both are formed by the tool rather than cut afterwards.
Threads need a way out of the mould. The external thread releases with a simple split. The internal one is the problem: a rigid core cannot simply be pulled through a threaded bore. The usual answers are an unscrewing mechanism, a collapsible core, or a thread form shallow enough to jump off. Which one is used changes the tool cost and the cycle time, and it is decided before steel is cut, not after the first trial.
The screen is a dense field of moulded holes rather than a separate mesh welded in. That choice shows up everywhere. A moulded screen cannot delaminate or come loose the way a welded mesh can, its holes are consistent from part to part, and it survives dishwashers. The cost is in the tool: hundreds of small pins, each one a potential hang-up on ejection or a burr that blocks a hole.
Hole layout is set by flow as much as by filtration. Holes packed too densely starve the melt between them and leave the last-formed region short; laid out in a pattern with feeding channels between groups, the screen fills cleanly and the flow rate through it stays even. On a tea strainer the difference is visible the first time it is used: an even screen drains, an uneven one pools.
The two moulded buttons on the rim are locating features, not decoration. They press outward against the inside of the bottle neck and snap into corresponding recesses, which keeps the insert from spinning when the lid above is tightened. Without them, tightening the lid would simply spin the strainer, and the internal fitting below would unwind with it.
They are moulded as spring features: shaped so they deflect inward on assembly and recover once past the recess. The force balance matters. Too stiff and the insert is hard to seat; too soft and it spins under torque anyway. The geometry comes from the bottle neck drawing, which is why we ask for it rather than sizing the buttons from the insert alone.
The tint hides tea stains and scale between washes, which is why these inserts rarely mould in water-clear material. The resin still has to be food-contact rated for the destination market and able to take repeated hot liquid and dishwasher exposure without cracking around the thin screen holes, which is where a part like this usually fails first if the material is wrong.
Thread form, gauged with the actual mating fitting and lid rather than a ring gauge alone. Screen hole quality under magnification, looking for burrs and blocked holes. Button snap force and resistance to spin under tightening torque. Flow rate through the screen on a sample, since a strainer that drains slowly gets blamed on the tea.
Kunshan Maifeng Precision Industry Co., Ltd. reviews drinkware part designs before quoting, builds the injection molds in house, and molds single-color and dual-color parts on 36 machines from 90 to 700 tons. Send us the bottle neck drawing and the thread specification, and we will come back with a feasibility comment and a tooling proposal.
Kunshan Maifeng Precision Industry Co., Ltd. (MIF) has an investment of RMB 35 million and an independent factory of more than 5,000 m². The company operates 36 single- and dual-color injection molding machines from 90 to 700 tons, together with more than 50 sets of mold manufacturing and processing equipment. Our service, management and production team includes over 100 people.
Our parent company was established in 2008. We provide product design, mold design and manufacturing, injection molding and product assembly services for custom plastic parts, supporting both domestic and international customers.
1. Product Design
Product structure design and optimization based on customer drawings and samples.
2. Mold Design
Mold design developed around product geometry, material and production requirements.
3. Mold Manufacturing
Machining, polishing, fitting and assembly for custom injection molds.
4. Injection Molding
Single- and dual-color injection molding for project and order requirements.
5. Product Assembly
Supporting assembly services for molded plastic components.
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