BS ISO 3353‑1:2020 pdf download.Aerospace — Lead and runout threads.
1 Scope
This document specifies the lead and runout requirements for rolled external threads for aerospace construction, and the inspection method to be used in case of dispute.
It is applicable whenever it is referenced in a definition document.
2 Normative references
There are no normative references in this document.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following addresses:
— ISO Online browsing platform: available at https://www.iso.org/obp
— IEC Electropedia: available at http://www.electropedia.org/
3.1
lead thread
portion of the incomplete thread that is fully formed at the root but not at the crest which occurs at the beginning end of either external or internal threads
3.2
runout thread
part of the screw thread in which is located the thread incompletely formed during rolling, between the completely formed threads and the part which has not been rolled
3.3
completely formed thread
thread, the profile of which (ABC) is located, over an axial distance of 1P, within the limits specified in the definition document for the thread
Note 1 to entry: See Figure 1.
4 Symbols for threads
d the major diameter of the thread
d 2 the pitch diameter of the thread
d 3 the minor diameter of the thread
P the thread pitch
5 Requirements
5.1 General requirements
The flanks at the root of the incompletely formed threads shall be joined by a radius or by two radii and a flat, that are smooth and devoid of abrupt tool marks. This radius, or these radii and the radius r (see Figure 3 to Figure 9) shall be greater than or equal to the minimum root radius specified for the complete threads in the definition document for the thread.
5.2 Lead threads
See Figure 2.
The possible profile projection comparator inspection shall be carried out using a chart drawn in
accordance with Figure 11.
5.3.2 Pitch diameter shank
See Figure 5.
6 Inspection method
6.1 General
The method is left to the discretion of the manufacturer, provided that it ensures conformity with the requirements given in Clause 5.
In case of dispute, the method by optical projection, defined hereafter, shall be used. See
comments in Annex A.
6.2 Use of the charts
The charts shall be used in conjunction with a profile projection comparator having a magnifying
power equal to or greater than ×20.
6.3 Procedure
6.3.1 For lead threads
The inspection shall be carried out using a chart drawn in accordance with Figure 10.BS ISO 3353‑1 pdf download.