Shenzhen Alu Rapid Prototype Precision Co., Ltd.

Step 1: Define requirements (e.g., ergonomic grip, 500g weight, aluminum material).

Step 2: Research 3D printing for initial model, CNC machining for final version. Get a quote from Shenzhen Alu Rapid.

Step 3: Design in Fusion 360, ensuring proper dimensions.

Step 4: 3D print a plastic version to test shape; outsource CNC-machined aluminum version to Shenzhen Alu Rapid.

Step 5: Test durability and fit on a car door mock-up.

Step 6: Refine design if handle is too heavy or slips, then rebuild.

Step 7: Document and prepare for injection molding if moving to production.