Instrument Rack Screw Locations
Horizontal Separation of Screws: 18-1/2"
Vertical spacing of screws: Small dimension is 1/2",Larger spacing is 5/8"

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Vertical Spacings:
          Width          Screw Sparation; Distance From Top/Bottom Edges to Screws    
1U        1-3/4"             1-1/4";               1/4" 
2U        3-1/2"             1-3/4";               7/8"
3U        5-1/4"             2-1/4";              1-1/2"
4U        7"                 4"    ;              1-1/2"
5U        8-3/4"             5-3/4";              1-1/2"
XU        X(1-3/4") = Y"     Y" - 3" (exceptions: 1U & 2U)
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0 -hole
1/2" ----- <---End of 3U------
0 -hole
5/8"
0 -hole
5/8"
0      <---screw
1/2"
0 -hole
5/8"
0 -hole
5/8"
0 -hole
1/2"
0     <---screw
5/8"
0 -hole
5/8"
0 -hole
1/2" ----- <---End  of 2U -------Start of 3U------
0 -hole
5/8"
0      <---screw
5/8"
0 -hole
1/2"
0 -hole
5/8"
0      <---screw
5/8"
0 -hole
1/2" ----- <---End of 1U--------Start of 2U ----------------------
0       <---screw
5/8"
0 -hole
5/8"
0       <---screw
1/2" ---- <---Start of 1U------------------------------
0 -hole