Moicstiy 25Pcs Steel Multi Grip Rivet Nuts Pre Bulbed Shank Zinc-Plated Flat Head Threaded Insert Nut Construction Fasteners for Industrial

Getting reliable threads into thin, awkward, or soft materials is always a challenge. In my shop, pre-bulbed rivet nuts are a go-to for these problem areas, and Moicstiy’s pre-bulbed inserts have earned a spot in that kit. They’re a simple idea executed well: a long, slotted steel sleeve with a flange that collapses into a broad “bulb” behind the workpiece, creating a strong, captive thread where you couldn’t put a nut or tap a hole.

What these inserts are (and the key specs)

This set includes 25 zinc-plated steel, pre-bulbed, flat-flange inserts sized for 1/4-20 machine screws. Each insert measures about 28 mm (1.1 in) in overall length and is intended for a 9 mm (0.35 in) drill hole. The “multi-grip” design lets them set securely across a wide range of material thicknesses, from thin sheet to moderate plastics and woods.

A quick note on specs: my set is definitely 1/4-20. You may see M6 x 1.5 referenced in some listings elsewhere, which conflicts with the packaging. If you buy these, confirm the thread size before committing to a project—an easy check with a 1/4-20 screw or thread gauge avoids headaches.

Build quality and corrosion resistance

The inserts are yellow zinc plated (“gold” in the listing), with consistent plating inside and out. Threads were clean in my batch—no galling or residual plating flakes—and I didn’t encounter any cross-threading with standard 1/4-20 hardware. Zinc-plated steel is the sensible middle ground for shop, automotive interior, and general construction use. It’s not marine-grade stainless, so for constant salt exposure or exterior structures that will see years of wet cycles, I’d step up to stainless plus-nuts. For typical indoor/outdoor DIY and vehicle use, the plating here is fine.

The flange is a simple flat head, not countersunk, so it sits proud on the surface. That’s desirable for load distribution, but if your application demands a flush finish this style isn’t the one.

Installation: what worked best

Pre-bulbed inserts need more travel and force to set than standard, short rivet nuts. You can set them three ways:

• Heavy-duty rivet nut tool with a long-stroke mandrel
• Dedicated plus-nut setter
• The classic bolt, washer, and nut method with hand tools

I used all three depending on access. A standard rivnut hand tool can run out of stroke before these lock down; if your tool’s mandrel is short, plan on the bolt-and-washer method. Here’s the routine that gave me the most consistent results:

1) Drill and size the hole. A 9 mm bit is the right call. In plastics and thin laminates, I’ve undersized by a hair and carefully reamed to reduce wobble. Deburr both sides—burrs prevent the flange from sitting flat and reduce grip.

2) Dry fit. The insert should slip in snugly but not require force.

3) Lube threads lightly. A drop of oil on the tool’s mandrel or the setup bolt helps you get a smooth, controlled pull without tearing threads.

4) Prevent rotation during the initial set. These have a smooth flange without knurls or anti-rotation ribs. In thin, glossy materials, I’ll pinch the flange with pliers during the first quarter-turns to keep the body from spinning until the bulb forms.

5) Compress in stages. Whether using a tool or the bolt/washer method, work in controlled pulls. Watch for the telltale increase in resistance when the bulb fully seats. Don’t over-crush—you’ll mushroom the hole or deform thin sheet.

6) Verify. Back the tool out and check that the insert doesn’t spin with moderate torque on a screw. If it does, you didn’t set it fully—give it another small pull.

For the bolt/washer method, a 1/4-20 grade 8 bolt with two heavy washers and a nut as a jam works well. It’s slower but extremely predictable and perfect in tight spaces where a bulky setter won’t fit.

Performance across materials

• Thin aluminum sheet: This is where these shine. In 0.040–0.080 in aluminum, I got a wide, even bulb that spread load nicely. Once set, I could torque a 1/4-20 screw to a reasonable spec without any spin-out. They’re excellent for mounting brackets, seat bases, or accessory rails to thin panels.

• Plastics: Standard rivnuts often disappoint in plastic; they don’t have enough “footprint.” The pre-bulbed design here engages a much larger area. I used them in a thick polyethylene bin and a polypropylene enclosure with success. The key is to drill cleanly, avoid oversizing the hole, and compress just enough to seat the bulb. These held without spinning under moderate bolt torque.

• Wood and laminates: In plywood and MDF, these set well if the hole is crisp. The bulb bites into the backside veneer and resists pull-through better than a short rivnut. They’re a practical alternative to T-nuts when you can’t access the back to hammer prongs in, and they present a clean metal thread for repeated assembly.

Strength and practical limits

Without manufacturer load charts, I rely on common sense and a few test pulls. The long bulb spreads load, so pull-out resistance is strong for the hole size. The weak points are:

• Rotation in very thin, slippery sheet if you under-set them
• Over-torquing fasteners and breaking the bond between flange and surface
• Corrosion if used in harsh environments

If you expect high torque on the mating bolt, consider a larger washer under the bolt head or a threadlocker to reduce future torque requirements. For thin sheet metal, a dab of epoxy under the flange before setting can improve anti-rotation if you’re worried about future spinning.

Fit, finish, and consistency

I measured consistent body diameters and lengths across the pack. The slotted legs formed even bulbs with no tearing. Threads were uniform; my screws started by hand every time. The only nit to pick is that the flange face is smooth—knurled or ribbed flanges make initial setting easier in slick materials. Plan to hold the flange during the first part of the pull, and you’ll be fine.

Again, confirm thread size upon arrival. My box was true 1/4-20 as stated, and all 25 were usable.

Use cases where they’re particularly effective

• Vehicle interiors and sheet metal work: mounting panels, racks, and brackets where you can’t reach behind
• Thin aluminum boats and utility trailers: seats, cleats, accessory rails
• Equipment housings and enclosures: adding threaded bosses without redesigning a panel
• Plastic bins, tool cases, and shop fixtures: repeated assembly/disassembly without chewing up holes
• Home projects: cabinets, metal furniture, and decor where you want a clean, serviceable thread

If you’re only anchoring into thick, rigid steel, a shorter, knurled rivnut might be simpler. These pre-bulbed inserts come into their own in thin or soft substrates and in variable thickness situations.

Tips to get the most out of them

• Use a step bit for clean, round 9 mm holes, especially in thin sheet
• Deburr aggressively and ensure the flange sits flat before setting
• Control the pull—don’t try to “one-shot” the set
• Keep a longer-stroke mandrel on hand; standard rivnut tools can run out of travel
• For plastics, consider a slightly tighter hole and lighter compression
• If you need sealing, add a thin neoprene washer under the flange and a dab of sealant

Verdict

Moicstiy’s pre-bulbed 1/4-20 inserts do what this style of fastener is supposed to do: create strong, reliable threads in places a standard rivnut struggles. They’re well made, consistently sized, and the zinc plating is appropriate for most workshop and vehicle tasks. Installation is straightforward with the right approach, and even without a dedicated setter, the bolt-and-washer method gets you there.

I recommend these inserts. They’re an excellent value for anyone who regularly outfits thin sheet, plastics, or wood with serviceable threads, and the multi-grip design covers a wide range of applications without hunting for exact grip lengths. Just be mindful of two caveats: confirm you’ve got the 1/4-20 version before you start, and plan for a longer-stroke setting method. Address those, and you’ll have a dependable anchor that doesn’t spin, doesn’t pull out easily, and saves you from crawling behind panels to hold a nut.