A roller shutter slat comprising:
- a hollow chamber profile cut to a desired length from a longer length of foam filled aluminum strip, the hollow profile, viewed in transverse cross-section, comprising first and second main walls, both curved in the same direction, such that the outwardly facing surface of the first main wall is convex and the outwardly facing surface of the second main well in concave, the walls at one end of the profile cross-section being bent inwardly, toward each other to form a double walled hook having a straight shaft curving to a hook end, said curvature which extends toward the hook end being toward the concave main wall, the walls at the other end of the profile cross-section forming a pocket, open along that end of the profile, the pocket having a semi-circuit shaped bottom facing toward the opening and adapted to receive a hook, similar to the said hook, but of another cooresponding shaped slat, the side walls of the pocket adjacent the semi-circular shaped bottom being generally straight and generally parallel to each other, the side of the pocket adjacent the outwardly convex main wall formed by a sharp angle of the end of the outwardly convex main wall, the side of the pocket adjacent the concave main wall forming, with an extension of the outwardly concave main wall, a double-walled counter hook extending toward the convex main wall and adapted to hookingly mate with the said hook at the said one end, but of another, correspondingly shaped slat, the said profile having points along its surface which are adapted to engage guide surfaces of a guide shutter, wherein:
- (a) the thickness of the material of the aluminum strips is 0.28 mm, +0.02 mm or -0.05 mm.
- (b) the straight line chord length of the width of the convex main wall from its junction with the pocket to the location where it bends inwardly at the said one end is 31.5 mm, +0.05 mm or -0.05 mm,
- (c) the radius of curvature of the outwardly convex main wall is 38.0 mm, +4 mm,
- (d) the radius of curvature of the outwardly concave main wall is 21.0 mm, +3 mm,
- (e) the distance between the first and second walls at their closest point is 2.3 mm, +0.5 mm,
- (f) the hook, at said one end has a length of 5.2 mm, -0.3 mm, and the thickness of the hook, taken along a line from its straight shaft to its hook end is 2.9 mm, -0.3 mm, and the straight shaft of the hook extends at an angle relative to a plane through the shutter guide surfaces, of 8.degree., +3.degree. or -2.degree., when the hook is pushed as far as possible into the pocket of an adjacent slat,
- (g) the pocket has an interior thickness between adjacent side walls of 3.3 mm, -0.3 mm, and said pocket has a width from the semi-circular bottom to the said sharp angle with the outwardly convex side wall which is 5.35 mm, -0.3 mm, and the straight side of the pocket adjacent the counter hook extends at an angle of 8.degree., -5.degree., relative to the reference plane when the hook is pushed as far as possible into the pocket of an adjacent slat,
- (h) and the profile is shaped such that it fits between guide surfaces of a guide shutter spaced apart by 7.5 mm, +0.2 mm or -0.5 mm.