The invention discloses a gauge which comprises a gauge body. One side of the gauge body is provided with a V-shaped groove, the V-shaped groove comprises a horizontal plane and an inclined tangent plane, and the horizontal plane and the inclined tangent plane are provided with a through hole along an intersection line thereof. The gauge has the advantages that the structure is simple, operation is convenient, and when the gauge is used for quality detection of corner connectors, the qualified rate of products is improved, and the labor cost is reduced.