Abstract: A simple engaging device comprises a locating base with at least a longitudinal hole, and at least a locating stem with an engaging head and a joining part corresponding to the longitudinal hole. Two flat locating parts are oppositely disposed at two lateral sides of the longitudinal hole; each flat locating part has a slant plane, a first slender retaining projection, a step, and a second slender retaining projection; the slant plane makes the joining part easy to be assembled and is capable of tightly guiding the joining part to reach the first slender retaining projection at which the joining part can be retained firmly without loosening, and the step and the second slender retaining projection are capable of engaging with the joining part in case of the engaging head and the joining part being worn out.

Abstract: A simple engaging device comprises a locating base with at least a longitudinal hole, and at least a locating stem corresponding to the locating base with an engaging head and a joining part. Two flat locating parts are oppositely disposed at two long sides of the longitudinal hole; each flat locating part has a slant plane, a first slender retaining projection, a step, and a second slender retaining projection; the slant plane makes the engaging head and the joining part easy to be assembled and is capable of tightly guiding the joining part to reach the first thin retaining projection at which the engaging head and the joining part can be retained firmly without loosening, and the step and the second thin retaining projection are capable of engaging the engaging head and the joining part to the locating parts in case of the engaging head and the joining part being worn out.

Abstract: A hidden fastening device for boards comprises a female fastening part attached to a board, and a rotatable male fastening part attached to another board to engage with the female fastening part. The rotatable male fastening part further comprises a rotatable male fastening base with a base opening, a lock end opening, and a receiving groove, and a rotatable male lock disposed in the base opening with a male lock end at a front side thereof. The female fastening part further has a mount hole to engage with the male lock end to enable the female fastening part and the rotatable male fastening part securing to each other. The lock end opening communicates with the base opening, and the male lock end extends via the lock end opening to engage with the female fastening part. A trigger extending outward the male fastening base is received in the receiving groove when the rotatable male lock is in a state of retreating with the lock end being received in the lock end opening.

Abstract: A simple engaging device includes a locating base with a pair of through hole sets being joined to the facial side of a flat piece of modular furniture, and two locating stems being joined to the lateral side of another flat piece; each of the through hole set has a first through hole and a second through hole with a flat engaging part disposed in between and the through holes communicating with each other laterally; each of the locating stems extends an engaging head with an annular recess in between corresponding to the flat locating part, and the engaging head is inserted into the first through hole and pushed toward the second through hole with the flat locating part engaging with the annular recess for the two flat pieces being easily assembled to each other perpendicularly.

Abstract: A simple engaging device for modular furniture includes a hinge-shaped base located at a joint of two flat pieces of the modular with a stationary plate member attached to one of the flat pieces, a screw nut attached to the other flat piece, and a set screw with a handle engaging with the nut through a locating bore of the movable plate member of the base; the stationary plate member is disposed with the first cylinder sections, and the movable plate member is disposed with the second cylinder sections; the first cylinder sections and the second cylinder sections are lined up axially and positioned alternately with a pin inserted and pivotally joined to the cylinder sections. The two flat pieces are assembled with an angle in between other than the right angle after the nut and the set screw engaging with each other.

Abstract: A manhole cover mounting structure includes an outer frame fastened to a manhole box by screw bolts, the outer frame having an upright guide rod in each of a plurality of hollow peripheral locating blocks thereof, an inner frame adjustably fastened to the inner frame to hold a cover plate in flush with the road surface. The inner frame has a plurality of female screws fastened to peripheral lugs thereof to hold a respective hollow screw rod for the mounting of through bolts; thereby securing to secure the inner frame to the upright guide rod in each locating block of the outer frame.