According to the old standard DIN 158, internal and external thread are tapered. Today, the tapered internal thread is still in use according to the old standard. The thread is used on sealing screws, screw-in connectors and lubrication nipples. The flank angle is 60°.

DEUTSCHE NORM tuna 1997 Metric taper external and mating parallel internal screw threads.

DIN 158-2 specifies the standard method of gaging the products internal parallel thread. Utilizing Go / NoGo thread plug gage members representing the minimum and maximum limits of the products thread. -Prior to gaging threads, it is important that the gage and product are clean and free from burrs. -Screw the Go plug gage into the product.

Conical, metric male thread ACC. DIN 158. Conical outside threads for tube connections, with sealant (see page 10) sealing in the thread. Threads acc. to this norm are used for pipe connections with conical screw-in plugs size C, which are to screw into cylindric screw-in holes size Z, both acc. to DIN 3852 part 1 (see page 8 – 10).

The DIN 158 metric tapered thread has a flank angle of 60° and a taper of 1:16. The thread designation consists of four components: the abbreviation M, the external diameter in mm, the pitch in mm, and the addition "keg" to distinguish it from cylindrical metric threads.

DIN 158-2 METRIC EXTERNAL TAPER SCREW THREAD AND MATING INTERNAL PARALLEL SCREW THREADS - PART 2. GAUGING SYSTEM, USE OF GAUGES, CALCULATION OF GAUGE DIMENSIONS AND GENERAL FEATURES. PF threads are functionally interchangeable with BSPP. This is an old designations replaced with G. PT threads are functionally interchangeable with BSPT threads.

Scope and field of application. This standard specifies profiles, dimensions and methods of verification for general purpose metric taper external threads intended to be mated with parallel internal threads with a basic profile as specified in ISO/DIS 68-1.

According to DIN 158, only the external thread is conical (taper 1:16), the internal thread is cylindrical according to DIN 13. According to the old standard DIN 158, internal and external thread are tapered.

DIN 158-1 Metric taper external and mating parallel internal screw threads - Dimensions, tolerances and inspection

din 158-1:1997 Metric taper external and mating parallel internal screw threads - Dimensions, tolerances and inspection The document defines nominal sizes, limit deviations and limits of size and their verification for metric external taper screw …