the present invention generally referred to as numeral 10 unit 10 is formed of a covering 11 a first plurality or layer of wood planks 12 a second plurality or layer of wood planks 13 and a third plurality or layer of wood planks 14 covering 11 is formed of a series of parallel wood planks 15 each formed and interfitted with tongue 16 and groove 17 construction so as to provide an even flat dance surface 18 the end boards 15a and 15b are provided with flat edges 15c and 15d for purposes hereinafter appearing planks 15 are assembled to the plurality of planks 12 by recessed nails 19 and the planks 12 13 and 14 are assembled to each other by nails glueing or other well known wood bonding means not shown the individual planks 20 of plurality 12 are spaced in parallel arrangement and are perpendicularly disposed to planks 15 and planks 21 of plurality 13 are in spaced parallel arrangement and are perpendicularly disposed to planks 20 and planks 22 of plurality 14 are in spaced parallel arrangement and are perpendicularly disposed to planks 21 as best seen in fig2 it is to be noted that end portions 20a of planks 20 extends outwardly from side edge 15c of plank 15 and side edge 21a of plank 21 so as to form a tongue 30 end edge 20b of plank 20 is recessed from edge 15d of plank 15b and from edge 21b of end plank 21c so as to form groove 31 oppositely disposed from tongue 30 edge 20d of end plank 20e extends outwardly from covering plank edges 15e and edges 21d of planks 21 to form tongue 32 see fig1 and 2 edge 20f.