Cantilever hook
- Molded in one shot with the door or cover
- Beam length limits how stiff the catch feels
- Best when engagement cycles stay in the hundreds or low thousands
Molded part guide: latches
Injection Molded Latches
A latch is a cantilever hook that flexes once on assembly and may flex again every time the user opens the product. The beam root, the hook angle, and the resin pick decide whether it still snaps shut after a year.
The job
Hold closed until someone meant to open it
Latches show up on enclosures, drawers, battery doors, and automotive trim.
Most molded latches are cantilever snap hooks: a beam tied to the wall, a hook that catches a ledge or slot, and enough deflection to climb over the mate on assembly. The same geometry has to survive repeated opens if the product is serviceable, without cracking at the root or relaxing until the door rattles.
Retention force is not only beam stiffness. Hook angle, engagement depth, friction, and whether the mate can creep all matter. A latch that seals with a gasket loads the beam continuously, so creep shows up as a leak before the hook breaks.
Tooling follows the hook. A releasable latch with a shallow return angle can often strip from the mold. A true undercut for a permanent hook needs a side action, a lifter, or a split line through the hook, which adds cost that only makes sense when the latch must never be opened without breaking.
Failure modes
Why molded latches let go or crack
Design review usually checks these before steel is cut.
| Mode | Cause | Direction to fix |
|---|---|---|
| Root crack | Sharp inside corner where beam meets wall | Generous fillet on the tension side of the beam |
| Fatigue after many cycles | Strain at the root too high for the resin | Longer beam, thinner hook, or a resin with better flex fatigue such as acetal |
| Loss of retention | Creep on a loaded beam or shallow hook engagement | Deeper engagement, stiffer mate, or reduce continuous load on the beam |
| Slip past without latching | Hook too short or return angle too shallow for the tolerance stack | Increase engagement or tighten mate location with datums |
| Nylon latch feels loose in humid air | Moisture plasticizes nylon and lowers stiffness | Design for conditioned nylon or switch beam resin to acetal or PBT |
Hook angle
Releasable hook or permanent catch
The return angle trades user access against tool complexity.
- Shallow return angles let the hook release for service and often eject without a slide
- A near-vertical return forms an undercut that needs a side action or lifter in the tool
- Dual latches on long doors share load and reduce beam length on each side
- A finger pocket or external lever reduces strain when users pry with a tool
Latch types
Cantilever hook or sliding latch mechanism
Hooks dominate low cost. Sliders appear when force or sealing is high.
Sliding or rotary latch
- Hook moves parallel to the seal face, which helps gasketed doors
- More parts, slots, and wear surfaces to mold and assemble
- Common when the product must stay sealed under vibration
Drawing
What to send with a latch design
Include the mate part and how the latch will be exercised.
Assembly sequence: how the hook climbs the mate on first close
Target retention force or a pass/fail test if you have one
Expected open/close cycles over product life
Whether the latch also compresses a gasket or foam seal
Service access: toolless open, screwdriver slot, or destructive open
Mate part CAD or the ledge dimension the hook catches
Keep reading
Related guides
Snap fit theory and parts that use latches.
Cantilever snap fit
Beam length, strain, and hook geometry.
Cantilever snap fitSide actions
Slides and lifters for hook undercuts.
Side actionsSharp corner stress
Stress at the beam root.
Sharp corner stressAcetal (POM)
Fatigue-friendly latch resin.
Acetal (POM)Hinges
The pivot opposite many latches.
HingesEnclosures
Shell closure and sealing context.
EnclosuresConnector housings
CPA and TPA style secondary locks.
Connector housingsTolerance stack up
Hook engagement after molded variation.
Tolerance stack upMolded parts hub
Every part-type guide, grouped by family.
Molded parts hubFAQ
Questions about molded latches
Can you mold a latch with a 90 degree undercut?
Yes, with a side action or lifter. That adds tool cost and maintenance. DFM review compares that cost to a releasable hook angle that strips from the mold.
Our latch cracked during drop test but not during open/close testing.
Impact loads the beam faster than manual flexing. A sharper root, a weld line through the beam, or cold resin at the root are common causes. Send the failure part if you have it.
Should the latch be on the box or the lid?
Either works. Putting the beam on the larger, stiffer half often gives a shorter effective cantilever and more consistent retention.
Do you calculate retention force?
DFM feedback flags risky geometry. Final retention is verified on molded samples in your mate part, because friction and tolerance stack dominate the measured force.
Next step
Quote the latch with its mate part
Upload the door or cover CAD and the body it catches on. DFM feedback covers beam root, hook undercut, and side action need.