A buckle with an enhanced efficiency in removing a foreign substance is provided. The buckle includes: a plug; and a socket provided with an insertion opening into which the plug is to be inserted. The socket includes: a pair of front pieces disposed side by side in a width direction intersecting with an insertion direction of the plug; a back piece disposed to face each of the front pieces; and a bottom piece that connects each of the front pieces and the back piece. A slit defined between the pair of front pieces extends in the insertion direction from the insertion opening across the bottom piece and the front pieces of the socket. Due to the presence of the slit, a cross section of the socket intersecting with the insertion direction is in a C-shape.

A strap uniting device for a wearable device is provided. The strap uniting device includes a base, at least one guide protruded from the base, and at least one catching part protruded from the base, and constructed different from the at least one guide, and arranged parallel with the at least one guide.

A buckle assembly may include a first connection member, and a second connection member configured to receive at least a portion of the first connection member in order to removably connect the first connection member to the second connection member. The second connection member includes an outer frame defining a central opening that is configured to allow monitoring of alignment and connection between the first and second connection members.

There is provided a buckle including a plug and a socket. The plug includes a plug-side base part, a pair of leg parts, and a pair of engagement protrusions. The socket includes a socket-side base part, an upper plate, a lower plate, upper side wall parts, lower side wall parts, engagement stepped portions, slits, and guide surfaces. A dimension of the pair of engagement protrusions in the upward and downward direction is set to be greater than a dimension of each of the slits in the width direction.