bt is shaped steel.
Section steel is a kind of bar steel with a certain cross-section shape and size, and is one of the four major varieties of steel (plate, tube, type, wire). According to the section shape, the section steel is divided into simple section steel and complex section steel (special-shaped steel).
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The former refers to square steel, round steel, flat steel, Angle steel, hexagonal steel, etc. The latter refers to I-beam steel, channel steel, rail, window frame steel, bending section steel, etc.
BT diode is TVS tube, patch package TVS tube screen printing is BT. Screen BT TVS tube is only one of the TVS tube models (SMBJ18CA, screen BT).