How to describe specification of Screws
             
             There are several popular notations for screws so far , Metric , American and  British 

             Metric, eg. M4X20 
             M4 : Diameter 
             20 : length 

             American , eg.#6-32x3/4  ,
             #6 : diameter 
             32 : Pitches per inch , 
             3/4 :  length

             British , eg. 1/8-40x10 ,
             1/8 : Diameter
             40 :  Pitch No. Per inch
             10 : Length

          Screw Head Type

                                               
           FLAT/CSK     BINDING       OVAL        TRUSS          BRAZIER     PAN (IIS)     PAN (ANSI)

                                                            
            ROUND         BUTTON          PAN          CHEESE      FILLISTER        PAN             HEXAGON
                                                   FRAMING                                             WASHER          WASHER


           Screw Drive

          
           PHILLIPS         SLOT      PHILLIPS/SLOT    SIX-LOBE      SIX-LOBE     SIX-BOBE     SIX-LOBE
                                                                             TAMPER           SLOT             PLUS 
              
               POZIDRIV    POZIDRIV       SQUARE    SQUARE SLOT    PHILLIPS    TRIANGLE     DOUBLE V
                                    ROUND                                                      SQUARE
             
             Y-TYPE        TRI-WING        POPPER        H –TYPE     HEXAGON        5-POINT        S-TYPE
             
              8-POINT        SPLINE         SPANNER       CLUTCH      PHILLIPS       SLOT IND.    6-LOBE IND.
                                                                                                SLOT IND 

              Thread Type

                
              TYPE A            TYPE AB              TYPE B            TYPE BT (25)      TYPE BF          DRILL POINT

             
              TYPE C             TYPE 1(D)         TYPE 23             TYPE F           LEAD POINT        TYPE U