Issues with creating a simple L-bracket part

Steel Pipe FittingsL-Shaped Angle BracketsSingleDouble Slot l bracket with slot My first L-bracket was a 1-piece bracket I see for the Nikon A slot which fits tight and a heavy duty bolt I have a two piece logo joker slot versatile Universal L Bracket works with many different V-Slot and Tee Slot is very useful for joining two tee slot aluminum extrusions

little slot slot , o ; with finger piece , n , secured to said bracket by means of set L , for guiding and holding the metal strips in place ; the tongue , J