Creating Mating Parts

It’s not always possible to create your entire part in one piece. When you need to create mating parts and fit two or more pieces together to create one part, there are many different ways to approach the design. Here are some of the most common ways to create mating parts to help you decide which might be best for your mold.

Self-Mating Parts

Why create two separate molds when one will do the job? It isn’t always possible to create self-mating parts where two identical parts can be mated together, but it saves a lot of time and money when you can do it.

What are self-mating parts? They’re pieces that are identical when placed side by side but fit together when one piece is rotated in one direction.

Think about a box with a hinge on one side and a clip on the other. Traditionally, you would need two separate pieces. But if you design a single piece with one hinge pin and one latch post on one side and one hinge hook and one latch tab on the other, you can connect two identical pieces.

Cantilever Snap-Fits

When you can’t make self-mating parts, skip nuts and bolts by creating cantilever snap fits when possible. If you put a cantilevered lug on one part and an undercut or ledge on the other, assembling the part is as easy as snapping the pieces together. That can save you a lot of time and money on assembly costs compared to other methods for mating parts.

Mechanical Fasteners

Sometimes, screws are inevitable. Mechanical fasteners – also called mounting bosses – are designs built into plastic components that allow you to assemble the parts with thread cutting or thread forming screws. One component will have room for the screw head and the other will have room for the thread side.

When designing a part that requires screws, work your design around existing hardware. It’s significantly cheaper than creating your own screw to fit into your part.

Lips and Grooves

Lips and grooves are often used in conjunction with other types of mating parts to ensure a secure fit. It’s important to keep in mind draft angles when designing lips and grooves – you may need gaps in your lip and groove design to accommodate the draft angle required to eject the part from the mold.


When combining parts with two different materials, you can often use overmolding. If two plastics are compatible, overmolding creates a permanent bond without the need for additional assembly.

What does overmolding look like? Picture the rubber grip on the plastic handle of a toothbrush. Overmolding has a variety of uses that can help save on assembly time.

Family Molds

If you can’t create self-mating parts, but you have two parts that are very similar in size and made from the same material, you can create family molds rather than two individual molds. This allows you to make both halves of a part in a single mold, saving the costs associated with creating a secondary mold.

Learn More or Get a Quote Today

To learn more about mating parts or to get a quote for your next injection molding project, click here or call 1-888-893-1587. Universal Plastic Mold (UPM) offers expert full-service plastic injection in America and has more than 50 years of injection molding experience.

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