lab micropipette pen 3d model

Create a detailed 3D model of a functional promotional pen designed to look like a laboratory micropipette. The model must be modular and composed of multiple separate parts that can be 3D printed individually and assembled manually without tools. STYLE AND DESIGN: The pen should visually resemble a modern single-channel laboratory micropipette: - Large ergonomic top head - Push button at the top (plunger style) - Cylindrical central body with a decorative volume adjustment ring - Long tapered lower cone similar to a pipette tip holder - Side clip inspired by pipette finger rest - Clean, professional, scientific aesthetic - Smooth surfaces, slightly rounded edges FUNCTIONAL REQUIREMENTS: The pen must be retractable using a click mechanism: - First press: pen tip extends - Second press: pen tip retracts - Internal spring-based mechanism INTERNAL COMPATIBILITY: - Must fit a standard Parker G2 pen refill (98mm length, ~6mm diameter) - Must include space for a small compression spring (~20mm length, ~5mm diam