I just fitted a series2 bocca rail (12.5” black ) for someone to a WE GBBR , and it came with two barrel nuts one went straight on and the other barely a full turn so I assumed that was for AEG . Did neither of yours not come with two ? Or has the new one not turned up yet ?  
	 
 
	as for Specna , I fitted a HAO mk16 rail to mine with the aeg spec nut and it went on with no dramas at all .