Hi Rich, The -2A and -2B is the thread class (fit) and the *.75 probably means 3/4" deep full thread. The thread class doesn't mean much for hobby work, it's used in commercial work to designate fit quality only if required. If you've got taps to suit, they may or may not have the class marked on them. If not, they'll probably cut normal commercial quality loose threads, fine for hobby stuff. The UNC does not mean UNCa Jesse Livingston needs to come and make yer threads, much as he might like to. Cheers, Jeff Dayman Waterloo Ontario Canada ----- Original Message ----- From: "R.L. Roebuck" <rlr20@xxxxxxxxxxxxxxxx> To: <modeleng@xxxxxxxxxxxxx> Sent: Thursday, October 20, 2005 9:29 AM Subject: [modeleng] Off topic a bit: UNF and UNC threads > Hi there All, > > I'm used to what I would call 'normal' UNF and UNC thread designations, > such as 1/2"*20 UNF, but I've got a few things on a drawing that don't > make sense to me - I wonder if anyone could shed some light on them. > > I have a stud marked as being threaded 1/2-20 UNF-2A > > I have another stud marked as 3/4-16 UNF-2A > > I have a hole marked as 1/2-13 UNC-2B * .75 > > Does anyone know what the stuf after the UNF or UNC refers to? > > > Yours, > > > Rich. > MODEL ENGINEERING DISCUSSION LIST. > > To UNSUBSCRIBE from this list, send a blank email to, > modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line. > MODEL ENGINEERING DISCUSSION LIST. To UNSUBSCRIBE from this list, send a blank email to, modeleng-request@xxxxxxxxxxxxx with the word "unsubscribe" in the subject line.