What characterizes a tack weld?

A tack weld is defined as a short weld that generally serves to temporarily hold pieces of metal together during assembly prior to making a full weld. It is usually characterized by a length of less than 25 mm. This characteristic makes it an effective tool for positioning and stabilizing components without the need for a continuous weld, allowing for adjustments in alignment before the final welding process occurs.

In this context, a continuous unbroken bead of weld is more indicative of a full weld rather than a tack weld. Methods for joining heavy steel components typically involve more robust welding techniques like fillet or butt welding. A circular joint does not specifically relate to the definition of a tack weld, which focuses on the length and the function of holding components in place temporarily. Thus, the defining feature of a tack weld is its short length and temporary nature, aligning well with the first choice provided.