Last year, we received an order from a Japanese client-to make joint screws for a high-end assembly robot. The client's requirements were simple: M2×6 size, GR5 titanium alloy, allen head, mirror-polished surface. It seemed unremarkable, but the client added, "This is for children aged 6 to 12, who will repeatedly disassemble and assemble it every day. Think about how you'll handle this."
So, our technical team did three extra things.
First
The standard thread tolerance is 6H, but we proactively upgraded to 4H-tighter and less prone to stripping.
Second
The head groove depth was increased by 0.1mm compared to the standard. Because children's hex wrenches may not be precision tools, a shallow groove makes them prone to slipping. If they slip, children get impatient and might bite them-our technical team said this couldn't be allowed to happen.
Third
All sharp edges were chamfered to R0.2 or higher. Adults won't touch the edge of a screw, but children will-they like to hold parts in their hands and play with them repeatedly.
After the sample was sent, the customer tested it for two whole weeks-simulating an 8-year-old child disassembling and reassembling it ten times a day for seven consecutive days. The screw threads were intact, the head was not deformed, and the surface was as smooth as new.
The customer sent an email with only one sentence: "You've thought things through even more thoroughly than we have."
The people who make toy screws have one thing in mind: on the other end of this screw, a pair of small hands are being held.