The $1,200 Fastener Mistake: A Simpson Strong-Tie Lag Screw, Bolt & Tek Screw Checklist

Back in 2019, I was two years into running material orders for a structural framing crew. I thought I had fasteners figured out. Then I approved a purchase order for 200 Simpson Strong-Tie lag screws that were completely wrong for the connection we were building. Same diameter. Same length. Same brand. And completely unusable, because I'd ignored the one detail that mattered: what those screws were connecting.

$1,200 worth of galvanized lag screws, straight to the junk bin. The reorder cost us a week of schedule and a very painful phone call with the general contractor.

From the outside, buying fasteners looks like the easiest part of a project. The reality is that the wrong fastener can stop a job faster than a missing beam. Since that 2019 mess, I run through a five-step checklist before every fastener order. It's caught at least a dozen errors that would've cost a lot more than the first one. If you're ordering structural fasteners for a project — contractor, GC, or a homeowner who's suddenly in charge of a deck — these are the steps. The last one is the one most people skip.

Step 1: Identify what you're actually connecting

The 2019 mistake happened because I picked the fastener before looking at the base materials. There are really four combinations in structural work:

• Wood-to-wood. This is where Simpson Strong-Tie lag screws earn their keep. They need a pilot hole, but for heavy structural lumber connections, they give you real holding power, and they're designed to work with the rest of the Strong-Tie connector system.
• Wood-to-steel or steel-to-steel. This is where Tek screws come in. The self-drilling point goes through the metal without a separate pilot hole, which saves a huge amount of labor when you're installing hundreds of them.
• Steel-to-steel with a nut. That's Simpson Strong-Tie bolt territory — a threaded fastener that clamps two members together with a nut and washer. Different head, different thread engagement, different load path.
• Fastening into tapped holes or machined parts. That's what machine screws are for. They're an assembly fastener, not a structural framing fastener, and they're not interchangeable with rated structural screws.

The connection that cost me $1,200 had a steel plate in the middle. Lag screws can't drill through steel, and I hadn't thought about what the screw had to do physically. I'm not a structural engineer, so I can't speak to the load calculations in every situation. What I can tell you from a procurement perspective is that asking "what exactly am I connecting?" before opening the catalog prevents a lot of expensive surprises.

Step 2: Check the load requirements before you pick a size

Once you know the materials, check what the engineer or the approved plans specify for that connection. Not what you ordered last time. The actual drawing.

If you don't have plans, the manufacturer's literature is the next stop. For Simpson Strong-Tie, that's the product catalog plus the ICC-ES evaluation reports for the product line. The two key numbers are shear capacity and tension (withdrawal) capacity. They're listed by diameter, length, and material combination, and they tell you exactly what a fastener can carry.

I remember one job where I was "pretty sure" a 1/2-inch diameter was fine for a pergola beam. The plans called for 5/8-inch. If I remember correctly, the inspector caught it on the first visit, and we lost the better part of a day removing and re-driving supports. It wasn't the end of the world, but it was a $300 mistake that came from guessing instead of reading.

Checkpoint: has a drawing or a stamped detail specified the diameter, length, and rating? If not, stop and find one.

Step 3: Match the fastener family to the connection

This is where the product categories actually matter. "A screw is a screw" is the most expensive sentence in construction.

Simpson Strong-Tie lag screws

For wood-to-wood connections in structural framing, lag screws are the workhorse. The Simpson Strong-Tie lag screw line integrates with their connectors and brackets, which means the head sizes, diameters, and lengths line up with their hangers and angles. That's the argument for buying into one system: it all works together.

Simpson Strong-Tie bolts

When the connection needs a nut on the far side, you need a bolt. Simpson Strong-Tie bolt products are used for wood-to-wood, wood-to-steel, and steel-to-steel connections where clamping force matters. A bolt carries load differently than a lag screw, and the two aren't interchangeable.

Tek screws

Tek screws are self-drilling screws, and the name has become a generic term for them on job sites across North America. They're not a Simpson Strong-Tie-specific product, but they solve the steel-to-steel problem without pre-drilling. The drill point cuts through the top layer, then the threads engage. Huge labor saver. But I see people treat every self-drilling screw as interchangeable, and that's a mistake. Check the head type, thread, and structural rating.

Machine screws

Machine screws are for tapped holes or for mating two metal parts where the threads are the junction. They have a different thread profile than wood screws and are not designed to grip lumber. If the plan calls for machine screws, use machine screws.

Checkpoint: does the fastener product you're ordering match the exact type referenced in the plans or evaluation report?

Step 4: Check the coating — and don't polish it with an angle grinder

This step cost me $450 in 2023, and it's the one most people miss.

Simpson Strong-Tie fasteners come in multiple finishes: zinc plating, galvanized, stainless steel, and Quik Guard coating. The right one depends on the environment — exterior, interior, coastal salt air, pressure-treated lumber. Match the coating to the connector. A galvanized connector with zinc-plated bolts is a corrosion mismatch that'll fail years before it should.

Now, about the angle grinder.

A guy on our crew asked me once if he could polish surface rust off a batch of galvanized bolts with an angle grinder before installation. Can you polish with an angle grinder? Physically, yes. But it was the wrong question. Grinding or wire-wheeling galvanized bolts strips off the zinc, which is the sacrificial coating protecting the steel. The light rust he was trying to fix was the zinc doing exactly its job. We didn't realize until he'd cleaned all 86 bolts, and we had to replace every one.

People assume that rust on a galvanized fastener is a defect. What they don't see is that the zinc is corroding first so the steel underneath stays intact. If a fastener shows heavy rust before installation, replace it. If it's light surface oxidation, leave it alone.

I'm not a materials engineer, so I can't walk you through corrosion rates. What I can tell you from a contractor's perspective is that replacing installed fasteners costs around ten times what the original order did.

Checkpoint: does the coating match the connector and the exposure? And don't "clean up" fasteners with a grinder.

Step 5: Plan the delivery date — and pay for certainty when it matters

The last step of the checklist isn't about specs. It's about when the parts actually land in your hand.

In March 2024, we had a structural tie-in with a hard deadline. The GC's schedule gave us a two-day window; if we missed it, the crane wasn't coming back for three weeks. I found a supplier selling Simpson Strong-Tie bolts about 15% cheaper than our regular distributor, with an "estimated" delivery of four to six days. Our distributor offered a guaranteed two-day turnaround for about $150 more.

I went with the discount. It was a mistake. The shipment arrived on day seven.

We ended up paying $400 for expedited shipping from the distributor to get the bolts on site in time. The "$150 we saved" became $400 of extra spend, a frantic Thursday, and a GC who still brings it up. The math I should have done upfront: certainty is worth something, and in an emergency, it's worth a lot.

If you're ordering against a deadline, you're not buying a fastener. You're buying the date it arrives.

That applies to Tek screws, machine screws, and Simpson Strong-Tie lag screws just as much as bolts. The cheapest price isn't cheap if the delivery date is a guess.

Checkpoint: is the supplier's delivery date a commitment or an estimate? Which one does your schedule need?

Common Mistakes I've Documented So You Can Skip Them

Here's the short list of errors I've personally watched happen in the last six years:

• Reordering "what we used last time." The bracket changed, the screw didn't follow. That mistake was 160 pieces of the wrong-length Strong-Tie lag screw, about $780, now in a bin we may never touch. What I mean is: always check the current drawing, even for a repeat order.
• Assuming any structural screw will do. A rated connection is based on a specific screw, specific diameter, specific steel grade, and specific coating. A lookalike from a generic fastener tray is not the same product.
• Believing "probably on time." "Probably" is not a delivery date. I've made this mistake more than once, and it never gets cheaper.
• Angle-grinding the coating off coated fasteners. It looks harmless for thirty seconds. Then you've turned a protected fastener into a liability.

My experience is based on maybe 150 material orders for wood and steel framing projects, give or take. If you're working in heavy fabrication or international sourcing, some of this won't translate. But the core checklist — materials, load, fastener family, coating, delivery date — applies at any scale.

I still kick myself for that 2019 order. But I'm glad it happened early, before we had a project where the stakes were a lot higher. The checklist costs thirty minutes per order, and it's saved me thousands. So glad I built it when I did.