A crimping device for securing a seal member onto overlapped end portions of a strap material includes at least a tool head, operating and stationary handles, two rows of crimping elements having at least a pair of shears and oppositely situated pair of jaws extended between the pair of shears. The crimping elements may be disposed in the tool head and connected with the handles so that at least one row of crimping elements crimps a seal while at least one row is idle when the handles move away from each other. In an embodiment, the handles can make an inward stroke only when a full jaw-closing outward crimping stroke is completed. At least one row of crimping elements crimps the seal with an inward movement of the handles while at least one previously actuated row of crimping elements is not involved in closing the seal.