So the pads/through holes labled: ground, 5V, and X/Y/Z. Are just placeholders. You must bridge those pads/holes to their relevant pads on the IC (if you want to use them). It was just an easy way solder a pin then be like oh there is "blank" in the furture and not have to look at a sheet with all 40 pins.
The idea here is to add header pins then and add the appropriate socket then sandwhich this thing inside your console or whatever so you can breakout the pins without directly soldering to the pins.
My specific uses for this will be to feed the outputs of various ICs in order to reverse engineer them.
|2||HDR-M-2.54_1x1||J1,J2,J3,J4,J5,J6,J7,J8,J9,J10,J11,J12,J13,J14,J15,J16,J17,J18,J19,J20,J21,J22,J23,J24,J25,J26,J27,J28,J29,J30,J31,J32,J33,J34,J35,J36,J37,J38,J39,J40||LABLED OVAL SOLDER PAD 120X60 MILL||40|