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This is a fillet profile. The slightly curved bottom of the profile is what epoxys we epoxied on to the fin can. To ensure that this curvature matched that of the fin can, we created a circle sketch the size of the fin can, and used a small section of that circle to base our fillet off of. The straight edge on the left is what sits flush against the fin. The top left and bottom right edges were rounded to improve the aerodynamics of the rocket. The length of the fillets varied depending what stage they were on; booster fillets were 8.5 inches long, whereas sustainer fillets were 5 inches long. 

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To make the transitions, we used 3D-printed PETG. 

Screws

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The team made a decision early on that as much as possible of the hardware should use torx head screws to limit the number of different kinds of screwdrivers required for integration. This presented a number of challenges for us as there were very limited options we could find for torx screws with the correct head type and correct length.

Requirements:

Pan or Button Head: We need the screw head to be as thin a possible so they would fit completely inside the fillet profile but couldn't use flat heads as there was not enough room to fit a countersink in the fillets