Here's a microscropic shot of style 120 showing the 4 harness satin weave
Another good example of a 4 harness satin weave is the predominately unidirectional cloth style 1543 which is an 8.6 oz/sq yd Fiberglass fabric that uses the ECG 75 1/2 yarn in the warp and ECD 450 1/2 yarn in the fill with a thread count of 40 x 39 ends/inch. Buy 1543 finished in 497A silane for any resin, soft 504 Volan for any resin or CS724 epoxy only finish.
A little closer in on the 1543 showing the 4 harness satin construction. The warp yarn is up and down, heavier and more concentrated than