This invention provides a method for inspecting a joined region and joining strength of a joined object formed by a spot friction stir joining process. In an optical recording method for recording information on a multilayer optical recording medium having a plurality of recording layers by irradiating the recording layer with a beam spot, any recording layer is set as an escape recording layer. To avoid the necessity of an interference fit, valve assembly positioning and stability is achieved by the use of an o-ring which is compressed by downward force exerted by a pressing cover upon a bushing or directly upon the o-ring. The device may also request and receive one or more IP subnets and corresponding IP addresses for each of its interfaces. In particular, a fabric made of Aramid or Nylon fibres may be used as the carrier material.