Threaded Flange
A threaded Flanges is used for special circumstances with their main advantage being that they can be attached to the pipe without welding.  Sometimes a seal weld is also used in conjunction with the threaded connection.  This special type of flange is generally used for high pressure, yet smaller diameter applications.  Obviously, the larger the flange is, the harder the ability to machine a thread would be.
Size
Threaded flange:1/4"-6"
DN8-DN150
Pressure
America Series:Class 150 ,Class 300, Class 600, Class 900A ,Class 1500,Class 2500.          
Europe Series:PN2.5,PN6,PN10,PN16,PN25,PN40,PN63,PN100,PN160,PN250,PN320,PN400.
Flange Facing Types
America Series:Flat face(FF),Raised face(RF),Tongue(T),Groove(G),Female(F),Male(M),Ring type joints face(RJ/RTJ)
Europe Series:Type A(Flat Face),Type B(Raised Face),Type C(Tongue),Type D(Groove),Type E(Spigot),Type F(Recess),Type G(O-Ring Spigot),Type H(O-Ring Groove)
Material
Carbon steel: ASTM A105,ASTM A105N,GB 20,C22.8.
Alloy steel: ASTM/ASME A234 WP 1-WP 12-WP 11-WP 22-WP 5-WP 91-WP 911
Stainless steel: ASTM/ASME A403 WP 304-304L-304H-304LN-304N
ASTM/ASME A403 WP 316-316L-316H-316LN-316N-316Ti
ASTM/ASME A403 WP 321-321H ASTM/ASME A403 WP 347-347H
Low temperature steel: ASTM/ASME A402 WPL 3-WPL 6
High performance steel: ASTM/ASME A860 WPHY 42-46-52-60-65-70
Standards
ASME ANSI B16.5,ASME ANSI B16.47.
API 605,API 6L.
MSS SP 44
CSA Z245.12
EN1092-1,EN1759-1.
DIN2566.
BS1560,BS 4504,BS 10.
AFNOR NF E29-200-1
ISO7005-1
AS2129
JIS B2220
UNI 2276. UNI 2277.UNI 2278 .UNI 6089 .UNI 6090
Industrial Processes
Die forging,Machining.
Application for threaded flanges
Natural gas,chemical,petroleum,ship building,marine,paper making, metallurgy, electric, power, boiler , etc.