grooves 50 54 when legs 74 78 are released they spring apart the ribs 66 68 on walls 44 48 of splines 58 62 slip into the grooves 70 72 respectively of grooves 50 54 to thereafter resist removal of splines 58 62 splines 58 62 may be nonetheless be removed from grooves 50 54 respectively because of their resilience if sufficient force is used ribs 66 68 and grooves 70 72 merely require intentional effort for their removal and are not removed for example as the result of say wind blowing on sheet 22 third groove 82 and cap 86 hide fasteners 90 from the exterior when cap 86 is fitted in third groove 82 fasteners 90 can be screws or nails dimensioned to pass from third groove 82 through lineal retainer 14 and into framing 10 far enough to hold lineal retainer 14 splines 58 62 and mesh screen 18 and sheet 22 even against brisk winds third groove 82 may be v shaped or have a v notch 94 cut in its floor 98 to identify and facilitate locating and driving of fastener 90 into lineal retainer 14 and framing 10 fastener 90 should pass from v notch 94 of third groove 82 through major axis a alternatively holes can be pre drilled into lineal retainer 14 when fastener 90 is seated in third groove 82 cap 86 can be set in place so no fastener 90 is exposed the.