  A quandle is an algebra with two binary operations satisfying three
conditions which are related to Reidemeister moves in knot theory. In this
paper we introduce the notion of the (canonical) tensor product of a quandle.
The tensor product of the knot quandle or the knot symmetric quandle of a
surface-link in $4$-space can be used to classify or construct invariants of
$1$-handles attaching to the surface-link.
