I evaluated my model view to find the best surfaces for starting my sketch. I confirmed that I can sketch on either the top rim of the chassis walls or the inside floor to create the corner pillars. I cleared up the math for my quarter inch top cover and quarter inch internal pillars, confirming they combine for a total depth of exactly half an inch. I planned to make the pillar holes go all the way through so that a half inch screw has extra safety clearance inside the car cavity instead of cracking the plastic. I selected the ISO 7380 hex socket button head screw. Its low-profile head keeps the top of my bumper car clean, and the hex drive provides good torque during assembly. I locked in the M3 size at 12 millimeters long, which safely fits the half inch total height while leaving a tiny safety gap at the bottom. I established the final numbers for my Inventor hole features. The top cover clearance holes will be 3.2 to 3.4 millimeters for a smooth fit, with enough flat space for the 5.7-millimeter screw head to sit flush. The pillar holes will be 2.5 millimeters so the M3 threads can bite directly into the 3D printed plastic.