Strenghtened plastic dolly

A plastic dolly comprising:

• a pair of longitudinal side members having end portions, each said end portion having an opening for receiving a caster bolt and having a groove formed longitudinally adjacent the outside end and along substantially the entire length of said longitudinal side member;
• a pair of transverse end members having end portions, said end portions having an opening for receiving a caster bolt;
• said end portions of both said longitudinal side members and said transverse end members interfitting to form a lap joint coupling said longitudinal side members and said transverse end members to form a frame, said lap joint being formed by overlapping substantially the entire said end portions of respective said longitudinal side members and said transverse end members and by mating an upper longitudinal recess of said longitudinal side member and a lower transverse recess of said transverse end member, said lap joints being securely fastened together at the corners of said frame, said end portions of both said longitudinal side members and said transverse end members are rabbeted and said end portions of said longitudinal side members are formed having longitudinal cutout portions and longitudinal projecting portions which form a space in which complementary transverse projecting portions of said end portions of said transverse end members can extend to their full depth along their entire length for strengthening said lap joint, said longitudinal cutout portion being a portion along the entire depth of each end of said longitudinal side member that is totally removed, wherein said upper longitudinal recess of said longitudinal side members encompasses substantially the entire area of said end portions of said longitudinal side members except for said longitudinal projecting portion, and said lower transverse recess of said transverse end members encompasses substantially the entire area of said end portions of said transverse end members except for said transverse projecting portion and said transverse end members have a length less than the distance between the outer edges of said pair of longitudinal side members, the reduced length being equal to the width of said longitudinal projecting portions of said end portions of said longitudinal side member;
• said longitudinal side members and said transverse end members being formed of high density polyethylene and being formed having a plurality of ribs extending substantially along their length and located on their undersides;
• reinforcement means for reinforcing and strengthening said longitudinal side members, said reinforcement means comprising a U-shaped metal channel disposed in each said groove and rivted to said longitudinal side member;
• reinforcement means for reinforcing and strengthening said transverse end members, said reinforcement means comprising a plurality of non-pyramidal-shaped ribs, said plurality of ribs combining to form a pyramidal-shaped cross section formed by providing said ribs with greater depths in the direction toward the center of said transverse end members to form a downwardly facing pyramidal shape;
• and
• locking devices disposed on the end portions of both said longitudinal side members and said transverse end members, said locking device comprising a locking projection and a locking slot wherein at least one said locking projection and at least one said locking slot are disposed on each said end portion of said longitudinal side members and at least one said locking slot and at least one said locking projection are disposed at corresponding locations on each said end portion of said transverse end members.