hole 16 is formed in the base or plate 11 of the support 10 the through hole 16 may have smoothly curved or radiused corners or edges 17 on opposite sides of the cord hole 16 forwardly and rearwardly thereof are located laterally elongate front and rear ladder openings or slots 18 and 19 respectively in adjacent spaced parallelism with the front and rear base edges 13 and 14 depending from the under surface of the generally flat base 11 peripherally bounding the circular cord opening or hole 16 is a circular ridge rim or rib 21 also depending from the under side of base 11 is a peripheral rim rib or ridge 22 bounding the forward ladder opening 18 similarly depending from a rearward region of the bottom plate or base 11 extending peripherally about the rear ladder opening 19 is a rib or rim 23 the forward region of forward depending peripheral rim 22 is provided with a depending extension or wall 25 and provided on its forward side with a downwardly tapering snap catch or retainer 26 the depending wall 25 may be coextensive with the lateral dimension of the depending rim or rib 22 and the snap finger or catch 26 may be laterally coextensive with the depending wall 25 also a.