3.125"
Just use your semi bolt to line it up when welding it up tot he side of the receiver through the holes.
Rich
The only legal way to attach the blocking bar is to weld it or use hi temp solder. No other option is legal according to ATF.
There we go again, someone who comes up with some B.S. information. The ATF is not a issue with my UZI builder, everyone enjoys their 2 cents worth, do you honestly think ATF is going door to door checking UZI builders.
:bs