the confined zone of the apparatus as noted above it is desired to have the width of the opening of the confined zone slightly greater than the width of the flattened tow 25 the width 34 w 34 can be adjusted by moving side plates 16 towards or away from each other which plates may be provided with slots 40 extending from the upper face 42 to the lower face 32 of the plates through which rods 18 pass thereby making the plates slidably engaged with members 12 and 14 the height 34 h 34 of the confined zone is defined by the height of the side plates 16 generally this height is in the range of between about 1 5 and 15 times the vertical thickness of the substrate being treated before it enters the application apparatus and is about 0 05 to about 1 0 inch as can best be seen in fig2 and 4 each member 12 and 14 respectively is provided with at least one cavity for each cavity present in the upper member there is a corresponding cavity present in the lower member having the same longitudinal axis the cavities may comprise essentially any shape such as a cylindrical bore or in the shape of a parallelepiped or a prism etc in the embodiment shown in the figures a cylindrical base is depicted as the cavity contained in each of the upper and lower members it is to.