Abstract: An attachment for connection with an elongated carpenter's level for forming an enlarged squaring tool, the level having a central web portion with spaced apart bubble indicators and parallel flanges at opposite end edges of the web portions. The attachment has an elongated arm member of rigid material with a connector arm fixed to and extending from it at a right angle. The connector arm has an elongated slot means forming a pair of spaced apart connector members, each having a peripheral cross section similar to but slightly smaller than the cross section of pockets located on opposite sides of the level web portion so that the connector members can be moved axially into said level pockets to firmly, but temporarily, secure the attachment to the level.