Industrial M27 Bolt Shift Knob for Thrustmaster TH8S

Description

Table of Contents

• Prototyping & Design Process

• All Prototypes & Grip

• Assembly Instructions

• Print Settings

"Industrial M27 Bolt" Shifter Knob – Thrustmaster TH8S / TH8A

Designed specifically for the Printables Thrustmaster Custom Shifter Knob contest.

The goal was to create a rugged, mechanical M27 bolt and nut shifter knob for sim racing, 100% 3D printed with zero metal hardware, perfectly fitted for Thrustmaster shifters using a dedicated custom adapter.

Prototyping & Design Process

• Prototype V1:

  • Bolt printing & thread post-processing: printed the 110 mm M27 bolt using organic supports. Despite dense tree structures, contact points remained minimal and the supports peeled off cleanly with pliers without damaging the external threads.

    

  • Nut fitment issue: the first nut prototypes had zero mechanical tolerance. Identical nominal dimensions caused immediate binding due to standard FDM plastic expansion, making it impossible to thread them onto the bolt and did I print all 5 of them at once before testing? Of course I did, so they are completely useless!).

    

• Prototype V2:

  • Thread clearance: added a 0.3 mm clearance on the internal threads.

  • Ergonomics: applied subtle chamfers along all hexagonal outer edges to eliminate sharp corners and soften palm contact.

  • Result: the nuts thread smoothly by hand along the entire 110 mm length of the bolt straight off the build plate.

    

• Prototype V2.1:

  • Print orientation & support optimization: tested build plate orientations to make support removal even easier. Printing the nuts lying flat generated a massive amount of support structures inside the central threads, which were tedious to clean out. Flipping the nut to rest on one of its outer hexagonal flat faces drastically reduced the supports to just a few minimal trees, keeping the internal threads perfectly clean straight off the plate.

    

• Final Version:

  • 100% 3D printed assembly: no brass inserts, grub screws, or extra metal hardware required.

  • Modular styling: stack 5 nuts in any color combination (e.g., Prusa Edition black & orange, Racing Checkered Flag black & white, or custom liveries).

    

  • Reliable mounting: reinforced adapter designed to lock firmly onto the Thrustmaster shaft under heavy shifting load.

All Prototypes & Grip

• Sequential & Rally Leverage: the 110 mm vertical profile offers a commanding grip and quick hand repositioning between wheel and shifter.

• Comfortable Hex Form: the edge chamfers remove bite points, allowing a firm palm rest during long endurance sessions.

• Customizable Weight & Look: run 5 nuts solid or space them out to alter grip height and cockpit aesthetics.

Assembly Instructions

1. Adapter: press/thread the printed adapter firmly onto your Thrustmaster shifter shaft.

2. Bolt: seat and secure the M27 bolt onto the adapter base.

3. Nuts: thread the 5 nuts onto the M27 shaft in your preferred color pattern.

4. Locking: tighten the nuts against each other to lock them in place at your preferred orientation.

Print Settings

• Printed on: Prusa Core One plus (0.4 mm nozzle)

• Material: PLA

• Layer height: 0.20 mm (Sturctural)

• Perimeters / Walls: 5 walls for the bolt and nuts

• Infill: 15% Gyroid for the bolt

• Supports: Organic / tree supports for the bolt shaft and adapter cavity

• Adapter: 100% infill (mandatory to handle shifting torque)

Tolerance note: All printers have different tolerances, we aimed to make a set of files that works on the maximum number of printers, but your mileage may vary. If your printer over-extrudes, slightly increase the XY Hole Compensation (+0.1 mm) or scale the nuts by +1% in X/Y.