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The contemporary square drive screw has all but replaced the Robertson screw proper and is commonly referred to as a Robertson because it has practically identical drive dimensions and the same colour identification system, but the contemporary square drive socket has parallel sides rather than tapered.
Slot screw drives have a single horizontal indentation (the slot) in the fastener head and is driven by a "common blade" or flat-bladed screwdriver.This form was the first type of screw drive to be developed, and, for centuries, it was the simplest and cheapest to make because it can just be sawed or filed.
Proper use requires that the screwdriver's tip engage the head of a screw of the same size and type designation as the screwdriver tip. Screwdriver tips are available in a wide variety of types and sizes (List of screw drives). The two most common are the simple 'blade'-type for slotted screws, and Phillips, generically called "cross-recess ...
Up-close image of the Robertson square-head screwdrivers. He had originally established his company, the P.L. Robertson Manufacturing Company, in Hamilton, Ontario in 1907. [ 3 ] [ 4 ] Robertson then relocated the company to produce his screws in Milton, Ontario , the following year after the town had given a $10,000 loan for the factory's ...
Square head cap screws up to and including 3 ⁄ 4 inch (19.05 mm) have a head 1 ⁄ 8 inch (3.175 mm) larger than the shank; screws larger than 3 ⁄ 4 inch (19.05 mm) have a head 1 ⁄ 4 inch (6.35 mm) larger than the shank. [9] In 1919, Dyke defined them as screws that are threaded all the way to the head. [10] socket screw
On a shaft, this may be simply a flattened area. A set screw may have any type of drive, such as hex or square head, slot, or recessed --- cross (Phillips), hex (Allen), star (Torx), or square (Robertson). In the UK, the term "set screw" or "setscrew" refers simply to a bolt which is fully threaded, with no smooth shank; called cap screw in the US.
Inch square-headed and hex-headed lag screws are covered by ASME B18.2.1. A typical lag screw can range in diameter from 4 to 20 mm or #10 to 1.25 in (4.83 to 31.75 mm), and lengths from 16 to 200 mm or 1 ⁄ 4 to 6 in (6.35 to 152.40 mm) or longer, with the coarse threads of a wood-screw or sheet-metal-screw threadform (but larger).
The square thread form is a common screw thread profile, used in high load applications such as leadscrews and jackscrews. It gets its name from the square cross-section of the thread. [ 1 ] It is the lowest friction and most efficient thread form, but it is difficult to fabricate.