Custom SBR Gasket (1mm thick) DXF Design

I need a CAD-ready drawing for a gasket that will be cut from 1 mm thick SBR on a CNC machine. The finished part must fit inside a 500 mm × 500 mm envelope, but beyond that the outline is completely open to creative, functional suggestions—I don’t have a sketch yet, so I’m counting on you to translate the functional requirements into a precise custom shape.

Here’s what I must receive:
• A clean, production-ready .dxf file, scaled in millimetres, that the CNC cutter can read without post-processing.
• All critical dimensions and any internal cut-outs clearly defined.
• A brief note or screenshot confirming overall size and material thickness so the workshop can double-check before tooling up.

I’m comfortable with whatever workflow you prefer—AutoCAD, DraftSight, Fusion 360, SolidWorks—so long as the final deliverable is a standard .dxf. Once the design meets the size limit and accounts for 1 mm SBR tolerances, we’re good to go.