1. 'TIS' (Tis) - The Safety Seal

TIS stands for "Thai Industrial Standard" and is issued by the Thai Industrial Standards Institute (TISI).

This is the most important mark indicating that steel is "quality." It has been inspected and certified to meet the required mechanical properties (e.g., tensile strength, elongation) and chemical composition.

• How to view it: The TIS symbol must be "embossed" on the steel (not printed) and includes the manufacturer's name, size, and grade.
• Why it's required: Without the TIS, we can't know whether the steel bar is strong enough to withstand the loads calculated by engineers. This is considered a very high risk.

2. 'Full Weight Steel' - Specifications Meet the Standard

"Full Weight Steel" is not an official term, but rather a term used in the industry to refer to steel that "100% meets TIS standards."

This means that if the TIS standard specifies that this size of steel must weigh 10 kilograms per bar, then "full weight steel" must weigh close to 10 kilograms (with a slight allowance for tolerances specified in the standard). Full weight steel is used by contractors and engineers for primary structural work requiring maximum safety.

3. 'Light Weight Steel' - Cheaper, but Riskier

"Light weight steel," also known as "incomplete steel" or "economical steel," is steel produced with a size, thickness, or weight "lower" than the TIS standards.

• Note: The price is significantly lower than "full steel" for the same size.
• Risk: Although it still bears the TIS symbol (in some cases, it may be a TIS or TIS mark for other types of steel), its load-bearing properties will be lower than standard.
• Applications: Some contractors may use it for non-structural projects, such as interior decoration, temporary fences, or structures that have been calculated by engineers to be able to support it. However, it must never be used for primary structural work (columns, beams).

Knowing and understanding these terms helps contractors select the correct steel for the job and communicate with vendors accurately. Choosing "full steel" with a clear "TIS" certification creates credibility and safety for your work.