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Adapters & couplers
Rigid shaft coupler, 5 mm to 8 mm
A rigid coupling that joins a 5 mm motor shaft to an 8 mm lead screw or output shaft in low-torque projects such as small linear stages or slow turntables. It is a 20 mm diameter cylinder 30 mm long with a 5.1 mm bore on one half and an 8.1 mm bore on the other, each with an M3 grub screw hole, and a solid web in the middle so the shafts do not touch. A D-shaped bore option locks onto a flatted motor shaft. Print standing up so the bores stay concentric. Open the ready-made model free, resize it on your phone or computer, then download a print-ready STL, 3MF or G-code sliced for your printer, free.Opening the ready-made model and downloading it as STL or 3MF are free, no card; AI changes use credits, from Maker at $7.99 a month.No printer? We print this part and ship it to your door. See its priceUpdated
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Adjust
Change its numbers in the viewer for free, or ask the AI in the chat: wall thickness, hole size, the thing it clips onto. AI changes use 2 credits per request (1 for a quick edit, 3 for a redesign), paid with a plan from Maker at $7.99 a month.3Print
Download a watertight STL or 3MF free, with your numbers and hand edits, or G-code sliced for your printer at the same price. After an AI change the download is included in every plan (4 credits without one).
Dimensions of the ready-made model (editable)
| Parameter | Value |
|---|---|
| outer diameter | 20 mm |
| total length | 30 mm |
| central solid web thickness | 2 mm |
| small shaft bore diameter | 5.1 mm |
| small bore depth | 14 mm |
| D-flat cut depth (into radius) | 2 mm |
| large shaft bore diameter | 8.1 mm |
| large bore depth | 14 mm |
| M3 clearance hole diameter | 3.2 mm |
| distance from each outer end to grub hole | 5 mm |
| outer edge chamfer | 0.5 mm |
Example prompt
Create a rigid shaft coupler 20 mm diameter, 30 mm long. One half has a 5.1 mm bore 14 mm deep with a 2 mm D-flat, the other an 8.1 mm bore 14 mm deep. One M3 grub screw hole per bore. 2 mm central web, 0.5 mm chamfers.
Fit notes
Shaft sizes in hobby motors and screws vary a lot, and SpeakCAD sizes each bore to your measured diameter with the clearance you prefer. Preview in the browser and ask for a longer body, a flexible slotted design or a D-flat in the chat.
Questions people ask about a rigid shaft coupler, 5 mm to 8 mm
A rigid coupling that joins a 5 mm motor shaft to an 8 mm lead screw or output shaft in low-torque projects such as small linear stages or slow turntables. It is a 20 mm diameter cylinder 30 mm long with a 5.1 mm bore on one half and an 8.1 mm bore on the other, each with an M3 grub screw hole, and a solid web in the middle so the shafts do not touch. A D-shaped bore option locks onto a flatted motor shaft. Print standing up so the bores stay concentric.
Click Open it free on this page and create a free account (no card): the ready-made model opens in your browser, on your phone or computer, nothing to install. Change its numbers in the viewer for free and download a watertight STL or 3MF free, or G-code sliced for your printer at the same price. An AI change in the chat uses 2 credits per request (3 for a redesign), and the download after it is included in every plan (4 credits without one). Start with Maker: 50 credits a month for $7.99, cancel anytime.
On this page: open the ready-made model free in a SpeakCAD account (no card), change any dimension in the viewer, then download the STL or 3MF free, or G-code sliced for your printer at the same price.
A shared STL is modelled for someone else's measurements. Here you open the ready-made model free, change it to your measurements in the viewer, then download a file sized for the part you actually own, free as STL or 3MF.
Yes. SpeakCAD slices the part on its servers with OrcaSlicer and your printer's official profile (380+ printers, including Bambu Lab, Prusa, Creality and Elegoo), and you download the G-code (a sliced .gcode.3mf for Bambu Lab printers). G-code sliced for your printer costs the same as the STL: included in every plan, free for a part you shaped by hand, 4 credits without a plan for a part with AI work in it. Pick your printer on the printers page to see its profile.
No. SpeakCAD runs in the browser on your phone or computer: the chat, the 3D engine and the live viewer load in the tab. The only file you download is the finished STL, 3MF or sliced G-code.
Print it your way
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