Characteristics:

Size and Shape: First-class bricks have a standard, uniform size (typically 242mm x 115mm x 70mm or 9.5" x 4.5" x 2.75") and a consistent rectangular shape with sharp, well-defined edges.

Color: They have a uniform reddish-brown or deep red color due to thorough burning.

Texture: The surface is smooth and compact, free from cracks or flaws.

Sound: When two first-class bricks are struck together, they produce a clear ringing sound.

Strength: They have high compressive strength, generally above 10.5 N/mm² (105 kg/cm²), making them ideal for load-bearing walls and structural work.

Water Absorption: These bricks have low water absorption, usually less than 10-11% by weight, which makes them resistant to moisture penetration and dampness.

Durability: 1st class bricks are weather-resistant and can withstand severe exposure to natural elements like rain, heat, and cold without deteriorating.

Usage: These bricks are commonly used in exposed masonry, facades, arches, and walls where high aesthetic appeal is needed. They're also suitable for foundational structures due to their strength.