The Everyday Symbol & Hallmark Reference
How to verify precious metal jewelry stamps, navigate food-safe plastics, and read tire expiration stamps like an inspector.
1. Precious Metal Hallmarks: Karats vs. Millesimal Fineness
When purchasing rings, chains, or vintage jewelry, microscopic stamps inside the shank reveal whether a piece is genuine solid precious metal or inexpensive electroplated brass.
| Metal Type | Stamp (Fineness) | Karat Equivalent | Purity % |
|---|---|---|---|
| Gold | 375 | 9 Karat (9K) | 37.5% pure gold |
| Gold | 585 | 14 Karat (14K) | 58.5% pure gold |
| Gold | 750 | 18 Karat (18K) | 75.0% pure gold |
| Silver | 925 / STER | Sterling Silver | 92.5% pure silver |
| Platinum | 950 / PLAT | Fine Platinum | 95.0% pure platinum |
2. Resin Identification Codes: Which Plastics Can You Heat?
The chasing arrows symbol does not automatically mean an item is curbside recyclable or microwave-safe. The number in the center (1 through 7) identifies the polymer resin:
- #1 PETE (Polyethylene Terephthalate): Water and soda bottles. Designed for single use only; repeated washing degrades polymer bonds, promoting bacterial harbor.
- #2 HDPE (High-Density Polyethylene): Milk jugs and detergent jugs. Highly stable and curbside recyclable.
- #5 PP (Polypropylene): Yogurt cups, takeout meal prep containers, baby bottles. The only common consumer plastic with high thermal resistance (up to 250°F / 120°C) suitable for reheating.
- #7 OTHER (Polycarbonate/Mixed): Exercise extreme caution with older containers, which may contain Bisphenol A (BPA).
3. Tire Sidewall DOT Date Stamps: The 6-Year Expiration Secret
Automotive tires deteriorate from chemical oxidation and UV exposure even if a vehicle is rarely driven. An old tire with full 10/32" tread depth can experience catastrophic sudden tread separation at highway speeds due to dry rot of internal steel bonding belts.
How to Locate and Read Your DOT Code:
The first digits represent factory and mold codes. The final 4 digits (2423) reveal:
- 24: Manufactured in the 24th week (mid-June).
- 23: Manufactured in the year 2023.
Related WhatMeans Standards & Lookups
Jump into our dedicated instant lookups and interactive tools:
Frequently Asked Questions: Everyday Stamps & Codes
What does 585 and 750 stamped on a gold ring mean?
These millesimal fineness numbers indicate parts per thousand of pure gold. 585 means 58.5% pure gold (equivalent to 14 Karat gold, with the remainder composed of alloy metals like copper, silver, or zinc for hardness). 750 denotes 75.0% pure gold (equivalent to 18 Karat gold). 999 or 24K signifies 99.9% pure gold.
Which plastic recycling numbers are safe for food and microwaving?
Plastics marked #2 (HDPE), #4 (LDPE), and #5 (PP - Polypropylene) are considered the safest for food contact. #5 PP is the primary plastic approved for microwave heat resistance. You should strictly avoid heating food in #3 (PVC), #6 (Polystyrene / Styrofoam), or #7 (Polycarbonate / Other), which can leach endocrine-disrupting chemicals and microplastics.
How do you decode the 4-digit DOT date stamp on a vehicle tire?
Look at the final four digits following the letters "DOT" on the tire sidewall. The first two digits signify the week of manufacture (01 to 52), and the last two digits represent the year. For example, "3822" indicates the tire was manufactured during the 38th week of 2022. Tires older than 6 years should be inspected annually, and tires past 10 years should be replaced regardless of remaining tread depth.
What is the immediate difference between a red vs yellow dashboard light?
Automotive warning lights obey universal traffic light color logic. Red lights (such as oil pressure or brake failure) signify a critical emergency—you must safely pull over and shut down the engine immediately. Amber or Yellow lights (such as Check Engine or low tire pressure) denote an active malfunction that permits cautious driving to a certified mechanic.