Stretcher bar / Stretcher frame for canvas paintings

Stretcher bar / Stretcher frame:
Material: pure wood
Two sizes:
1) 2 x 3 cm (actual size: 1.5 x 2.5cm)
2) 3 x 4 cm (2.5 x 3.5 cm)
There are two kinds of 3 x 4 cm stretcher, they are of different costs, please let us know your choice.
a). The normal kind, made out of whole timbers.
b). Made of jointed timber which is stronger.

Common use size and packing information as below:
60x90x4cm (24"x36"x1.5"), 0.026CBM/PC, 8PCS/CTN, 0.205CBM/CTN;
90x90x4cm (36"x36"x1.5"), 0.038CBM/PC, 8PCS/CTN, 0.305CBM/CTN;
50x100x4cm (20"x40"x1.5"), 0.024CBM/PC, 10PCS/CTN, 0.239CBM/CTN;

Stretcher bar / Stretcher frame for canvas paintings; Material: pure wood