BS 3A 210:2019 pdf free.Aerospace series -Nuts, hexagonal, ordinary and thin, Unified threads (below .250 inch), brass, tin plated – Specification.
5 Material and manufacture 5.1 The nuts shall he machined from free machining leaded brass bar in accordance with BS EN 12163, BS EN 12164 or BS EN 12167 alloy CW614N-R430. NOTE BS249 and BS2874 have been withdrawn but are included here for reference only Jor nuts machined from free machining leaded brass bar, alloy CZ121 Pb3-M. which might still be in service. 5.2 To maintain visual identification of a nut’s thread end with the non-countersunk face, deburring using a suitable barrelling method shall be the acceptable method to keep metal removal to a minimum. The sharp thread break-out shall not be deburred using hand or machine tools which use a cutting blade. 5.3 The nuts shall be configured in accordance with: a) Figure 1. for Ordinary Nuts; or b) Figure 2, for Thin Nuts. 6 Dimensions All finished nuts shall conform to the dimensions and tolerances given in Table1 or 2.
NOTE Unless otherwise stated, the values given are in inches. For a guide to the thread sizes converted to decimal inch and metric mm, refer to BS 350.
7 Screw threads The nuts shall have Unified threads of the form and fit specified in the relevant requirements of BS 4A 100. 8 Protective finish
All finished nuts shall be coated with tin in accordance with BS 1872, classification Cu/Cu/Sn/13/m.  9 Inspection procedure The nuts shall be inspected in accordance with the requirements of BS 4A 100. 10 Identification and marking 10.1 For the purposes of identification, the nuts shall be marked in accordance with the requirements and limitations of BS 4A 100, prior to applying the protective finish, with: a) the basic BS part No. identifier, e.g. A210;
b) the contiguous circles symbol, 000 to indicate the use of Unified threads; and c) when applicable, the use of left-handed threads, L. . 10.2 For ordering purposes, the nuts shall be designated with the full BS part number. The number (without spaces or hyphens etc.) shall consist of the BS identifier A210, appended with the BS Suffix Code listed in Tables 1 and 2. EXAMPLE 1: A 4-40 UNC Ordinary Nut with a standard RH thread, shall be designated A210AP
EXAMPLE 2:  A 4-40 UNC Thin Nut with a LH thread, shall be designated A210ATL.BS 3A 210 pdf download.