Admin Buyer FAQ: Loctite 641 vs 660, Super Glue Plastics, and What You Can Actually Mail

Straight answers from someone who orders all of it

I'm the office administrator for an 85-person company. On any given Wednesday I'm comparing industrial adhesives, sourcing client gifts, and trying to figure out whether a small package can go First-Class or needs Priority. Different budgets, different vendors, same person. Here are the questions I actually get asked—from coworkers, from other admins, and from the vendors themselves.

Jump to what you need:

• What can you actually mail in a standard envelope?
• Loctite 641 vs 660—which do I need?
• When is the Loctite Super Glue Plastics Bonding System worth it?
• Sourcing gifts like a Marc Jacobs mini tote or ladybug jewelry box
• Corporate gift compliance—what the IRS cares about
• Does adhesive expire?
• One vendor or many?

1. What can you actually mail in a standard envelope?

More than people think, but less than people hope. USPS defines a standard letter as 3.5" × 5" minimum up to 6.125" × 11.5" maximum, no thicker than 0.25", and under 1 oz. As of January 2025, a First-Class Mail letter costs $0.73. If it's rigid, has clasps, or is lumpy, it goes as a large envelope (flat) starting at $1.50, or it gets returned non-machinable with a penalty surcharge.

What you can send: documents, flat merchandise like stickers or fabric swatches, gift cards (inside a card, ideally), checks. What you can't: anything liquid, sharp, or fragile. Cash is technically legal but dumb—no tracking, no recourse. And under 18 U.S. Code § 1708, only USPS-authorized mail can go in a residential mailbox—a mistake that can run up to $5,000 per violation. Three jewelry pieces can fit flat in a padded envelope. Small boxes usually can't—check the 0.25" thickness rule first.

2. Loctite 641 vs 660—which do I need?

These get confused constantly because they're both retaining compounds, but they solve different problems. Loctite 641 is a medium-strength, removable compound for cylindrical fitting parts—bearings, bushings, press-fit pins. It fills small gaps, prevents fretting, and can be disassembled with hand tools when you need maintenance later.

Loctite 660 is the worn-shaft fix. Same general purpose, but it's a gap-filling compound—it handles coarse voids, scoring, and damaged keyways up to roughly 0.020". If your bearing seat is shot and a new bearing won't hold, that's a 660 job. If everything's within spec and you just want it locked, 641 is the right call. Buying 660 for new parts wastes money. Buying 641 for worn ones won't hold. I'm not a machinist—my maintenance lead walked me through this—but that's the practical split we use.

3. When is the Loctite Super Glue Plastics Bonding System worth it?

Only when you're dealing with low surface-energy plastics—polypropylene, polyethylene, PTFE. Cyanoacrylate alone won't grab those. The plastics bonding kit includes an activator pen that primes the surface so the glue actually cures.

For ABS, PVC, acrylic, or styrene? Skip it. Plain super glue is fine and cheaper. And here's the part that surprised me: for structural plastic repairs, CA glue is the wrong tool entirely—you want an epoxy or a methacrylate. The bonding system is a targeted fix for a specific surface-energy problem, not a general "better super glue." We keep one kit in the maintenance cabinet for the specific case of polypropylene housings. It's been opened maybe three times in two years. That's not a knock—it just tells you the actual frequency of the problem.

4. Sourcing corporate gifts—Marc Jacobs mini tote, ladybug jewelry box, that kind of thing

I get asked to source designer items more than you'd guess. A Marc Jacobs black leather mini tote is a $200–$400 line item depending on the model and where you buy. At that price, it's client-facing executive thank-you territory—not a general employee perk. Vendor sourcing matters too: authorized retailers offer returns, and you'll want a proper invoice for the expense report. I learned that one the hard way.

Smaller items like a ladybug jewelry box—usually $15–$60—are far more flexible. Employee birthdays, small raffle prizes, a thank-you add-on for a client's assistant. They ship cheaply in padded mailers, and customers actually keep them. The category works because it's small enough to be a sincere gesture and nice enough to not feel like a refrigerator magnet. I do have mixed feelings about branded swag vs. useful small gifts—the useful ones stick around longer, but they're harder to bulk-order.

5. Corporate gift compliance—what actually matters

The IRS treats business gifts over $25 per recipient per year as non-deductible above that threshold. That's per person, not per gift. So if you send a client a $200 tote, you can deduct $25 and you'd better have documentation for the rest—or just book it as a marketing expense and talk to accounting first.

Beyond tax: many public-sector clients and companies with strict procurement rules cap what employees can accept. A $40 jewelry box is usually fine. A $300 handbag can trigger disclosure requirements. I'm not a compliance officer—please loop yours in before sending anything pricey. What I can tell you from the admin side is that getting the invoice right the first time saves weeks. Vendor, recipient, business purpose, date. Missing any one of those and finance kicks it back.

6. Does adhesive expire?

Yes, and it's a real failure mode. Loctite anaerobics typically carry a 12–24 month shelf life from manufacture—printed on the tube or bottle. Stored in a hot warehouse past that date, they can fail to cure entirely. We lost a batch that had been sitting on a shop shelf through two summers. The parts came back loose two months after assembly.

Now we date-stamp incoming adhesive and rotate stock first-in-first-out. Cheap insurance. If you're ordering in bulk to save on shipping, factor in how fast you'll actually go through it. A 50ml bottle of retaining compound lasts our shop about four months. A 250ml bottle would expire before we finished it.

7. One vendor or many?

Many, and I'll defend that position. A general industrial distributor who "does everything" is going to be mediocre at adhesives, mediocre at electronics, and mediocre at corporate gifts. We buy adhesive from a specialist who knows shelf life and can answer technical questions. We buy gifts from a retail or promotional vendor who understands packaging and returns. The vendor who told me "this isn't our strength, here's who to call" earned my trust for everything else.

Consolidation has its place—it simplifies payment terms and reduces the number of accounts payable is juggling. We got down to six primary vendors from eleven and cut our AP admin by about four hours a month. But I'd rather juggle a couple of accounts than work with someone who pretends to be good at everything.

Look, there's no perfect system. What works is knowing which problems belong to which expert, and calling them before you guess.