First you might asked "why making such a tool?", if not you can go straight to how to make it :)

I often had the problem to screw mechanical parts together in a spot very hard to access, and sometimes the screw/washer fell and I was like « oh no, how will I get them back? » « will I be able to get them back? » So I made this really simple tool that greatly helps me, and I hope it'll help you too.

This tutorial will guide you, step by step, on how to make a custom version that will fit to your needs.

There is also a video tutorial too, I hope you will like it.

Supplies

a screw driver, in my case an Allen key
a screw
a washer
a sliding caliper
a 3D printer
a software like Fusion360 to draw the tool
a software like Ultimaker Cura to prepare the 3D printing

Step 1: Measuring

Using a sliding caliper is essential to get really good measurements and making the perfect tool.

Please refer to the pictures, 4 measurements are needed:

Allen key diameter (between two opposite summits): 3.44 mm
screw head diameter: 6.9 mm
screw head height: 4 mm
washer diameter (external one): 9 mm

Once the measurements are done, we can start to create the 3D model.

Step 2: 3D Modeling

This part assumes you can have basic knowledge in a 3D drawing software like Fusion360. No worry here, what we will do will be very simple: circles, extrusions and fillets, that's all!!

Please look at my video for a more visual step by step explanation:

Here are the step-by-step to follow:

Draw two concentric circles: a 11mm and a 3.74mm
extrude the part between the two circles with a 14mm value
selecting the top surface of the extrusion, draw a concentric 7.2mm circle
extrude -7mm with cut selected (removing material)
again, from the top part, draw another concentric 9.3mm circle
extrude -4mm with cut selected (removing material)
select each edge in contact with Allen key, screw and washer, and apply a 0.3mm fillet

Notice that I added 0.3mm to each diameter to be sure that the Allen key, the screw and the washer will be inserted properly. This 0.3mm value was found after a couple of tests. For exemple, after my first print the screw can't be inserted, so I increased the diameters by a 0.05mm step and print again. I had to do it a couple of time. Only several 3D printed tests will make the perfectly fitted tool (if you're lucky, yours will be OK from the first print). When inserted, Allen key, screw driver and washer must hold in place without falling or easily sliding. All these values can be adjusted, you can adapt the dimension to your needs, for example if your need a wider or longer tool.

Step 3: Preparing the 3D Printing

To prepare the 3D printing file I used Ultimaker Cura using the following parameters:

infill of 100%
extra fine resolution (0.06mm in my case)
I'm using PLA material, so just in case I added a skirt and heated the hot bed to 60°C/140°F
no support needed
a speed of 30mm/s (low)

For the extrusion temperature, look for the information regarding your filament specifications.

Step 4: Printing and Testing

I loaded the file in my 3D printer, and about 30min after the tool was ready for the first tests.

As I said, I had to print a couple of pieces before getting the one I needed. The tool must be able to:

slide along the screw driver or Allen key, but not to easily
hold tightly the screw and the washer

Step 5: Conclusion

Now you have everything you need to make this tool. I hope it will help you in your projects. Thank you reading or watching the video and send me comments if you need more information.