Knurled Insert Nuts, 50pcs M3 x 4mm L x 5mm OD Brass Heat Set Insert Nuts, Female Threaded Knurled Embedding Nuts for 3D Printing Laptop Automotive Plastic Shells

It worked as it should.

If you are tired of screws stripping out of plastic or want to build professional-grade 3D printed enclosures, these brass heat-set inserts from Sunkoo are a great choice. They provide strong, reusable machine threads for any project involving PLA, PETG, or ABS. Design and Installation The standout feature of these inserts is the aggressive knurling and the integrated guide. Easy Alignment: The small pilot or "guide" at the tip makes it much easier to keep the insert straight as you press it in with a soldering iron. This reduces the risk of crooked threads, which is a common headache with cheaper inserts. Uniformity: Out of the 100-piece pack, the quality is remarkably consistent. I didn’t find any with clogged threads or malformed outer diameters. Grip and Durability Compared to other M2.5 inserts I have used, these have a slightly larger "pitch" or more aggressive knurled surface. Pros: This larger texture provides a more substantial bite into the plastic. Once the plastic cools and shrinks around the brass, these inserts feel incredibly secure and resistant to being pulled out or spinning under torque. Cons: Because the outer knurling is a bit more substantial, they do require a slightly larger footprint in your 3D model. You’ll want to ensure your printed parts have enough wall thickness to accommodate them without bulging the exterior. Pros Superior Grip: Aggressive knurling makes them feel more durable than standard smooth-knurl inserts. Excellent Conductivity: Brass material heats up quickly and evenly for smooth installation. Clean Threads: M2.5 bolts thread in smoothly with no grit or resistance. Great Value: 100 pieces for roughly $7 is hard to beat for this level of quality. Cons Larger Footprint: Requires a bit more space in your design compared to "slimmer" M2.5 options. Final Verdict: 4/5 Stars These are high-quality inserts that prioritize strength and ease of installation over miniaturization. If you have the room in your design for the slightly larger outer diameter, the extra durability they provide is well worth it.

These are the most robust way to add threads to a 3D printed part. Design the part with a hole longer than the insert and wide enough to fit the tip (for the M2 size, a 3.7mm hole worked best for me), place the insert in the hole, and use the tip of a soldering iron to push the insert in. For a perfect flush finish on a flat surface, stop just before the insert reaches the surface, and use a flat metal tool to push it in the rest of the way so it stops perfectly flush (the insert will remain hot enough for this if you are quick about it). Doesn't get much easier than that! Once installed, you have durable metal threads that will survive repeated assembly/disassembly and won't strip out like threaded plastic, even under load. For the (very reasonable) price, you get a 100 pack which should be enough for many projects.

I do a lot of structural 3D printing relative to most people, plus some machining of plastics, so I go through inserts like this fairly regularly. So when these popped up, I figured I would give them a try. I don't regret it. They're good inserts. The dimensions are accurate, and the threads are clean. M6 fasteners thread in smoothly and fit snug. They heat evenly and set it nicely. I've used them in polycarbonate and HPDE now, and both have worked out nicely. They are very secure. For $8 (at time of review), a pack of 25 M6 inserts is a pretty good value considering the quality. Of course, if you need larger quantities of this over a longer period, then buying a larger pack is usually the way to go. This is good for small-scale/infrequent stuff. I have a problem regarding the marketing of this product, though. Most of the product photos are AI-generated, which itself isn't the problem. But if you look closely, there's stupid stuff like people handling red-hot inserts with bare hands and others using these inserts in metal engine blocks with a ratchet? Obvious AI slop, but it's just misleading, giving a certain perception that isn't accurate (or even relevant) to the product or its intended uses. Hopefully Amazon puts policies in place about that kind of thing sometime soon. Taking a star off of my otherwise 4-star rating for the misrepresentation.

I picked up this pack of M4 brass heat‑set inserts for a few 3D‑printed projects, and they’ve been exactly what I needed. The sizing is accurate, the knurling bites into the plastic cleanly, and every insert I’ve used so far has seated smoothly without deforming or spinning. The brass heats evenly and bonds well into PETG. Once installed, the threads feel strong and reliable with no wobble, and no surprise pull‑outs when tightening a bolt. I’ve used them for functional parts like brackets and enclosures and they’ve held up great. The quantity is perfect as I always will find something I need them for. Everything arrived clean, uniform, and ready to use. I wish they would have came in a little box so I can keep them with all the larger ones I have. These come in a small plastic bag. If you do any kind of 3D printing, small repairs, or plastic‑shell work, these inserts are perfect.

These are decently made insert nuts. The sharp edges help bite into the plastic for a strong grip. The only downside is that the threads are a tad bit on the loose side, though they are fine for most practical uses. I verified the count was, in fact, 100 pieces and the dimensions are as stated.