din-7991-vint参考标准资料

UDC621.882.215.61.091.6January 1986西Hexagon socket countersunk head cap screws7991Senkschrauben mit InnensechskantSupersedes May 1985 edition.In keeping with current practice in standards published by the International Organization for Standardization (ISO),a comma has been used throughout as the decimal marker.Dimensions in mm1 Field of applicationThis standard specifies product grade A hexagon socket countersunk head cap screws with ISO metric screw threadfrom size M3 up to and including size M24.If,in special cases,the screws are to meet requirements other than those given in this standard,e.g.with regard toproperty class or material,these shall be selected in accordance with the appropriate standard.This also applies to thefine pitch thread conforming to DIN 13 Part 13 required in exceptional cases.As a consequence of the head geometry and the form of the wrench engagement,the critical cross section of screwscovered by this standard is located below the hexagon socket and not in the thread.It is thus recommended that thescrews should not be used for the transmission of high axial loads involving prestressing.If a DIN 911 double offset screwdriver is used to tighten the screws by way of their socket,the torsional strength andthe design of the key only permit the application of prestressing loads corresponding to about 80%of the prestressingloads specified for the commonly used property class 8.8 screws.DimensionsChamfered end complying with DIN 78.Slight rounding or countersinkat the mouth of the socketpermissible (no further than e).(b)ds is applicable only for screws with unthreaded portion of shanku 2 P maximum;incomplete thread.Detail XEdge radiusedor flat.Continued on pages 2 to 6366