The tubes of a heat exchanger core are interlocked and spaced from are another prior to brazing in a furnace. Each of the separate plates of each tube is formed with discrete laterally spaced tabs which project transversely to the plane of the plate for spacing and for locking adjacent tubes with one another. These tabs are an integral part of stamped plate and are bent so that they are generally perpendicular to the plane of the plate. The locking tabs have a flat, upturned locking end that is resilient to closely fit over the end of an adjacent plate of an adjacent tube to interlock adjacent tubes together. Straight spacer tabs are used to spaced separate tubes from one another. These spacer tabs are similar to the locking tabs but have straight abutment ends instead of the flattened locking end portions to provide column support. With the locking and spacing tabs in place, the tubes are arrayed in a core which is securely interlocked and accurately spaced.