V1 Magnetic Needle Guide + Injection Assist for Insulin / GLP-1 / TRT

2/22/2026 Update: V2 Injection Assistant is now available.  Get that one!

Overview:

Injecting myself makes me anxious.  This device takes away most of the stress by giving me an ergonomic grip on the syringe and automating the injection motion with magnets.

After adding the syringe, push up the sled until the embedded magnets snap it into place.  While holding the guide against your skin, push down gently on the actuator and the sled will smoothly jump to the lower set of magnets while inserting the needle.  The syringe plunger will be within easy reach without adjusting your grip.

2/15/2026 Update:  Based on feedback and prints, I've updated and simplified the Shell options and instructions.  New standard shell has all of the benefits of prior versions with improved ergonomics and assembly.

2/20/2026 Update: PTFE cutting jig .stl added

Compatibility:

Pick a shell based on needle length:

• Standard shell is compatible with 6mm, 8mm, or 12.7mm / ½" needles 

• “Tall” shell supports longer needles up to 1" or 25mm

• “X-Tall” shell supports needles up to 1.5" or 38mm

Syringe adapters available:

• 0.3ml (30 unit) U-100 syringes

• 0.5ml U-100 syringes

• 1ml U-100 syringes

• 1ml Luer Lock syringes

• 2ml BD Emerald Luer Slip syringes

• 3ml Luer Lock syringes

These are the specific U-100 syringes I modeled this on: https://a.co/d/9yr9vVx 

and these 1ml Luer Lock: https://a.co/d/67SUaba 

Common uses are Insulin, GLP-1 (Semaglutide / Tirzepatide), TRT (testosterone / hormone replacement therapy), or B-12 injections.

Printing and assembly:

Total assembly takes less than 5 minutes.  All magnets are press-fit and shouldn't need any glue

1. Print all parts as oriented in the files.  No supports are needed.  You'll need:

   1. One Shell (your choice and depending on the length of the needles you use)

   2. One Sled

   3. One Syringe Adapter

   4. One Plunger

   5. (optional) PTFE cutting jig

2. Sled Assembly:

   1. Press in 3 magnets.  2 on the rear and 1 on the bottom. (take care that both rear magnets are facing the same direction)

   2. Align PTFE with the slots on the side and press in.  You can insert it while long and then cut flush with the top after OR pre-cut with the PTFE Cutting Jig.

   3. Attach the Syringe Adapter using 2 M3x6mm screws

   4. Attach the Plunger to the top of the sled using the M3x20mm screw.

3. Shell Assembly:

   1. Press in 3 magnets.  The polarity should be aligned so all three are attracted to corresponding magnets on the sled

      1. TIP: To easily insert the bottom magnet with the correct orientation, attach an extra magnet to the bottom of the sled, then insert the sled into the shell and press down.  It will align and press in the magnet for you.

   2. Optional: Add a strip of scotch tape to the inside/rear wall of the shell running vertically over the magnets.  It makes for a very low-friction surface for the sled.

   3. Insert the sled from the top.  It should slide smoothly with no interference.  If your magnets are oriented correctly, you'll feel it stop when the sled is flush with the top of the shell.  Pushing it further, it should snap smoothly to the bottom position.

You're done!

Tips: 

1. If the sliding motion feels stiff, check the the PTFE tube is fully pressed into the sled from the sides.  Try pressing the side of the sled/tubes against a table to ensure that it's not bulging out.

2. Stiffer / thicker wall PTFE tube seems to have a more reliable shape and make for a more frictionless slide.  I used 2mm ID, 4mm OD tube and it worked well.  I have some thin 3mm ID tube that didn't work reliably at all.

3. You can fine-tune the sled by trimming/rounding off the bottom lip /  cut edge ff the PTFE after it's inserted into the sled

BOM / You will need:

• 2  X  M3x6mm button head screws 

• 1  X  M3x20mm screw (Or M3x30mm for “Tall” option)

• 6  X  6x3mm magnets ( https://a.co/d/00Z1qbCi )

• about 4" / 100mm of 2mm ID / 4mm OD PTFE Teflon tube ( https://a.co/d/3ThyJNc )