Update 4: Rufus is now 17 weeks old and weight about 35 lbs. This harness is still functioning well even through leash training (which includes a lot of pulling and correction, and the buckles are still showing no signs of wear). I am about to just a new strap of webbing because the old one is now too short. I'll keep you updated on how long and far this set-up works on a yellow lab as he grows up.

I have a new Puppy. He needs some kind of restraint, and I feel like a collar is not good for his neck. The green webbing you see in the photos is on sale at Amazon, and the D-ring is cheap at Hobby Lobby. I found several buckle models here on Thingiverse, and I used them to create this model of a 3-way buckle with slip-locks. It's worth giving full credit to Thingiverse contributor "salman272885." His original Thing was instrumental in my making this 3-piece buckle:

https://www.thingiverse.com/thing:6374727

The models here include:

• the assembly model, which you should not attempt to print.
• The main receiver model, which you should print vertically as the model is oriented. The additional skirt is in the model to add adhesion to avoid it pulling off your plate while printing in this orientation. The point here is to put the layer lines around the body of the main receiver for the sake if strength.
• The Male Connectors are modeled together in one file so they can be printed together. Left and Right are indicated by the ">>>" and "<<<" on the top face.
• The friction buckle should be printed in this orientation with slicer supports added as there is a plate-facing surface not flat against the print plate. You will need two of them.
• The uploaded models DO NOT include the spacer I made to add Rufus' name and my phone# (which is now adequately pixelized 😉). You can easily add these yourself using Tinkercad or your favorite modeling app.

Assembly notes:

• I printed these using PLA. I tried a version using TPU, but TPU is not rigid enough to stay buckled. I am never successful in printing in ABS, but I suspect there's an ABS version of this model that would be durable enough for a pet larger than 30lbs. If we could print this in Tin or Aluminum, it would be a great harness for any furry friend.
• You should cut the webbing based on the size of your pet. Cut the length to be about 25% more than you think you need.
• Pull the webbing through your "D" ring and fold the webbing in half to trap the "D"-ring in place.
• Offset the halves into a slight "V" shape - about 10° to allow the halves to do what's necessary to put this gear on your pet. I hand-stitched the ring in place. If you have a heavy-duty sewing machine, you could stitch it up in a pretty robust way.
• Instructions on how to thread the webbing have now been uploaded.

To strap your pet in:

• Face your pet (pet your pet, don't be a monster).
• Hold the harness with the receiver up and the ends hanging down.
• Lay the receiver on your pet's back with the female end facing your pet's tail.
• Drape the strap with the RIGHT SIDE connector over your pet's LEFT SHOULDER, then draw it back on their chest and connect to the RIGHT SIDE on the receiver.
• Drape the strap with the LEFT SIDE connector over your pet's RIGHT SHOULDER, then draw it back on their chest and connect to the LEFT SIDE on the receiver.
• This should cause the harness to create and "X" on their chest, securing your pet in the harness.
• Make sure the connectors audibly CLICK.