The 5-Step Checklist That Saved Us $18,000 in Silicone and Rubber Part Mistakes (And How You Can Use It Today)

If you've ever ordered a dow corning silicone grease or a batch of rubber O-rings and ended up with parts that don't fit, leak, or fail after a week—you know the feeling. I've been there. More times than I'd like to admit.

I've been handling procurement for rubber and silicone parts for 6 years. In that time I've personally made (and documented) 12 significant mistakes, totaling roughly $18,000 in wasted budget. The worst one was a $3,200 order of custom gaskets that looked perfect on the drawing but turned out to be made from the wrong material. We caught it only after production shut down for a day.

Now I maintain our team's checklist to prevent others from repeating my errors. Here's the exact 5-step process I use—every single time—before placing an order for silicone rubber, grease, gaskets, washers, or O-rings.

Who This Checklist Is For

If you're responsible for sourcing any of these items, this is for you:

• Engineers or buyers ordering custom rubber/silicone parts
• Maintenance teams stocking spares for pumps, valves, or fittings
• Anyone who's ever confused a gasket with a washer with an O-ring

This checklist has 5 steps. Follow them in order, and you'll catch 90% of the common mistakes I've seen (and made).

Step 1: Define the Operating Environment (Don't Just Look at the Drawing)

Conventional wisdom says: draw the part, send the drawing, done. My experience with over 200 orders says otherwise. The first thing I ask now: where will this part live?

What to check:

• Temperature range – Silicone can handle -60°C to 200°C, but standard NBR rubber starts degrading above 100°C. If you're sealing hot oil, you need something like FKM (Viton).
• Chemical exposure – Silicone grease (like dow corning silicone grease) is great for valves and electrical contacts, but it won't stand up to solvents. I once used it on a fuel system—cost us $890 in redo plus a 1-week delay.
• Pressure & vacuum – O-rings for static vs dynamic sealing need different durometer ratings. More on that in Step 4.

Mindshift here: I used to think any rubber is rubber. Now, I always confirm the environment first—even if the customer says "just match the old part."

Step 2: Measure the Real Dimensions (Never Trust the Part Number Alone)

We once ordered 1,200 O-rings based on an existing part number. They fit—barely. The wrong cross-section made the seal fail after three cycles. The savings? Minimal. The cost? $1,200 wasted.

Your dimension checklist:

• For O-rings: inside diameter (ID) and cross-section (CS). Standard sizes follow AS568 (inch) or ISO 3601 (metric).
• For gaskets: ID, OD, thickness, and hole pattern if it's a flange gasket.
• For washers: ID, OD, thickness—and note whether it's a flat washer, cupped, or spring washer. They're not interchangeable.
• For silicone rubber sheet: length, width, thickness, and durometer.

Pro tip: I always measure the mating groove, not just the old part. Parts can be compressed or stretched after removal. If possible, use a caliper—not a ruler. If I remember correctly, a 0.5mm error in ID on a small O-ring can cause a leak.

Step 3: Pick the Right Material (Silicone vs Rubber vs … You Name It)

This is where most of my expensive mistakes happened. The question is not just "silicone or rubber?" but which specific compound fits your application.

Here's a quick cheat sheet based on what I've learned the hard way:

Material	Best for	Watch out
Silicone (VMQ)	High/low temp, food contact, electrical insulation	Poor abrasion resistance, not for dynamic oil sealing
Nitrile (NBR)	Oil, fuel, hydraulic fluids	Degrades above 120°C, not good for ozone/UV
EPDM	Weather, steam, water, brake fluids	Not compatible with petroleum oils
FKM (Viton)	High temp + aggressive chemicals	Expensive (3-4x silicone), limited flexibility

Real example: On a $2,500 order for silicone rubber gaskets for a steam line, I specified standard 70-durometer silicone. The gasket failed in two weeks because silicone isn't rated for continuous steam exposure (EPDM would have been correct). Saved $200 by not upgrading—cost $4,000 in the end including downtime.

Step 4: Confirm Hardness (Durometer) – The Most Overlooked Spec

Everything I'd read said durometer is for engineers, not buyers. In practice, I found that it's the most common source of field failures. A 70 Shore A O-ring feels about the same as a 90 to untrained fingers—but their sealing behavior is night and day.

Rule of thumb:

• 50-60 Shore A – soft, good for low-pressure seals, can handle some misalignment
• 70 Shore A – general purpose (the industry default for most O-rings)
• 80-90 Shore A – hard, used in high-pressure applications, less compression set

I once ordered a batch of dow corning silicone rubber sheets with 50 durometer thinking softer = better sealing. For our high-pressure application, the material just extruded into the gap. The part failed and we had to scrap 100 units.

Check this: Always ask the manufacturer for the durometer range on the test certificate. If they can't provide one, find another supplier.

Step 5: Verify the Standard (Don't Assume 'Standard' Means What You Think)

The words "standard O-ring" can mean different things to a US supplier vs an Asian one. And don't get me started on gasket vs washer vs O-ring confusion.

Quick clarity:

• Gasket – a static seal between two flat surfaces (flange, pipe joint). Usually custom-shaped or cut from sheet.
• Washer – a thin ring used to distribute load, prevent loosening (spring washer), or seal (bonded washer). Not designed for dynamic sealing.
• O-ring – a torus-shaped seal used in a groove, can be static or dynamic.

Standards to ask for:

• O-rings: AS568 (inch) or ISO 3601 (metric) – include dash number. Example: AS568-214 means 1.049" ID × 0.103" CS.
• Rubber sheets: ASTM D2000 line callout (e.g., 2AA710) defines material and hardness.
• Silicone grease: specification like MIL-PRF-23827 or food-grade NSF H1 if needed.

My biggest facepalm moment: I ordered "silicone grease" for a vacuum system without checking the outgassing spec. The dow corning silicone grease we got was standard high-vacuum grade? No. It was a general-purpose compound that contaminated the chamber. The rework cost us $3,000. The right product was there all along—I just didn't ask the right question.

3 More Mistakes to Avoid (Bonus Warnings)

Here are a few things that burned me but didn't make the main list:

1. Don't mix materials in the same order without clear marking. We ordered silicone and NBR O-rings in the same batch. They weren't labeled. The technician installed NBR in a high-temp zone—melting, leak, fire risk. Cost: $2,500 in rework + a safety report.
2. Don't skip the sample. Even with a detailed spec, the first production piece might not match. Always request a first-article inspection (FAI) for critical parts.
3. Don't assume the cheapest quote is the best. Saved $80 on a small batch of gaskets by choosing a budget vendor. The actual material was a different durometer than specified. The reprint cost more than the original "expensive" quote.

Final thought: The checklist above came from 12 real mistakes—some small, some embarrassing, all educational. The most frustrating part was knowing that most of them could have been avoided with a 10-minute pre-order review. Now I'm sharing it so you don't have to learn the same way. Take it from someone who's been there: use this list, save yourself the headache.