THE AUSTIN-HEALEY 100 SIX (Series BN6)

Fastener Codes

Introduction

This section describes the fasteners used on the Austin Healey, and the relationship between the fastener part numbers found in this Parts List and the type of fasteners used.

The following sections and tables were originally published in Austin-Healey 100/100-6/3000 Restoration Guide, Appendix One by Gary Anderson and Roger Moment, and are reproduced here by kind permission of the authors.

Thread Systems

There were five basic thread systems of British fasteners. British Standard Whitworth (BSW) was a coarse thread system used on hex-head bolts and screws. Whitworth fasteners were only used in a few applications on the four-cylinder cars, such as attaching the adjusting link to the generator front plate, and were not used on the six cylinder cars. On the Hundreds, the fine-thread fasteners were threaded to the British Standard Fine (BSF) standard. In addition, a British Association Standard Thread (BA) system was used on smaller screw sizes, most typically on the fuel system.
    In 1954, a new "Unified" system was introduced that used Unified National Coarse (UNC) and Unified National Fine (UNF) standard threads on bolts. UNF bolts were gradually introduced to replace BSF bolts and the changeover was largely complete before the six-cylinder Healeys went into production. UNF and UNC threads are respectively compatible with American Society of Automotive Engineers (SAE) and United States Standard (USS) hardware, though there are some fine differences in the actual thread contours.
    With the changeover to the Unified system, a scheme for marking fasteners was developed to allow them to be easily distinguished visually. Hex head UNF screws and bolts have a circular dimple in the center of the head. An alternative marking to these is stamping connected circles on one of the hex flats. UNF nuts were marked using a circular groove in one end face or stamped connected circles on one hex flat. Wheel stud nuts have a notch cut into the corners between hex flats. UNF studs have a protruding circular stub on the end.
    The relationship among bolt specifications is shown in the following table:

TABLE A1-1
Bolt Specifications by System
 
Shank tpi tpi Wrench Size tpi tpi tpi Wrench Size
Diameter BSF BSW BSW BSF UNF SAE USS UNF BA tpi
0.110 6 47.9
0.142 4 38.5
3/16” 32 24 3/16W 1/4BSF 32 32 24 5/16 2 31.4
1/4 26 20 1/4W 5/16BSF 28 28 20 7/16
5/16 22 18 5/16W 3/8BSF 24 24 18 1/2
3/8 20 16 3/8W 7/16BSF 24 24 16 9/16
7/16 18 14 7/16W 1/2BSF 20 20 14 5/8
1/2 16 12 1/2W 9/16BSF 20 20 13 3/4
*Note: The 3/16 screw diameter is the same as a Number 10, as in 10-32
 

    The quickest way to identify original UNF hex bolts is to look for the circular dimple. If you don't find the dimple, and the bolt doesn't have the radial line markings found on American bolts, it is likely that it will have a BSF or BSW thread. A thread gauge should be used to verify the thread pitch and the type of bolt.

Applications

BSF fasteners will be found on engine, transmission, steering, front suspension, and spiral bevel axles on BN1s. UNF bolts appear on the gearbox casing of BN2s. The six-cylinder engines use UNF (instead of BSF) bolts, as do steering components. The bolt attaching the adjusting link to the front plate of the generator is BSW on BN1 and BN2 cars, and may also be on six-cylinder series.
    As noted above, BSF fasteners would be more common on early (1953) cars, gradually being phased out and replaced with UNF. From 1955 on, except as noted, UNF is definitely the predominant fastener, with BSF hardware almost extinct on the six-cylinder cars. One way to tell which type a fastener should be is through the parts book, where BSF screws, bolts, and nuts will have a BMC part number (e.g., 2K 8558) while UNF ones use the coded system described above (e.g., HBZ 0410).
    BA screws will be found on fuel pumps, carburetors, and distributors of BN1s through BJ8s. They are also used for a few other applications, such as mounting the top pivot of BJ7/8 vent windows to the window frame.

Codes and Markings

The Service Parts List is a good source for details on what types of screws, bolts, nuts, and washers to use in each application, since the parts numbers in the Parts List specify exactly what size, finish, and type of fastener to be used at almost every point in the car. The most comprehensive source for information, and the one used to compile this appendix, is the Austin Service Journal, Volume 25 - Cars, "Repairs Data" p. 23 which gives detailed descriptions of UNF fasteners along with drawings and dimensional specifications. Nevertheless, there are still some fasteners that are not clearly noted in the parts lists; here the restorer needs to take careful notes of the type of fastener and codes on them so that they can be put back from where they were removed.

Manufacturers

Manufacturer's markings are usually present on the heads of hex bolts. The following markings have been found on original pieces: Auto, Atlas, BAX, Bees, CL, Cranes, CRF, CRS, FB FCF, GKN, GSF, JF, Linread, Marwin, Newton, Richards, RO, RSB, Ruberry-Owen, SA, SN-JH, SN-MW, Sparts, Torrington, TWL WF, WI, Wiley, Woden, Unbrako.
    A rating code is often found along with the manufacturer ID. These codes include: R, B, D, V, S, and T. In addition, some bolts will be found that have no manufacturer identification, but perhaps just the rating code.

Parts List Codes for Fastener Identification

An identification system is used that allows one to determine the fastener type, shaft diameter, and length from the listed part number. It applies to screws, bolts, washers (flat and lock), and nuts and covers all UNF fasteners, but not BSF hardware.
    Those part numbers that use the code comprise three letters describing the head type, fastener type (bolt, screw), and plating, though the order of the letters varies, and a series of numbers that specify the dimensions of the bolts and screws, and the dimensions and characteristics of washers and nuts.

Codes for Bolts and Screws

For bolts and screws, the three letters indicate the type of screw or bolt and the type of plating, and the last three or four digits specify the dimensions. The first two digits specify shaft diameter in 1/16-inch increments for both bolts and screws. The last two digits specify the length in 1/8-inch increments for hex-head bolts and screws, and in 1/16-inch increments for slot-head, Phillips, and Pozidriv screws. For example, HBZ 0409 is a hex bolt, zinc-plated, 4/16 inch (or 1/4 inch) in diameter by 9/8 inch (or 1 1/8 inch) long, while HNS 0409 is a hex screw, also zinc plated and of the same dimensions. PPP0407 is a pan-head chrome-plated Phillips screw, 1/4 inch in diameter by 7/16 inch long.
TABLE A1-2
Type Codes for Bolts and Screws
 
Letters Type Plating Comments
HBN Hex Bolt Plain
HBZ Hex Bolt Zinc
HNS Hex Screw Plain
HZS Hex Screw Zinc
HPS Hex Screw Chrome End of Screw is pointed
HPN Hex Screw Plain End of Screw is pointed
HPZ Hex Screw Zinc End of Screw is pointed
PMN Pan-head Screw Plain Phillips or Pozidriv
PMZ Pan-head Screw Zinc Phillips or Pozidriv
PMP Pan-head Screw Chrome Phillips or Pozidriv
PPN Pan-head Screw Plain Phillips or Pozidriv, Pointed
PPZ Pan-head Screw Zinc Phillips or Pozidriv, Pointed
PPP Pan-head Screw Chrome Phillips or Pozidriv, Pointed
CMN Flat-head Screw Plain Phillips or Pozidriv
CMZ Flat-head Screw Zinc Phillips or Pozidriv
CMP Flat-head Screw Chrome Phillips or Pozidriv
CPN Flat-head Screw Plain Phillips or Pozidriv, Pointed
CPZ Flat-head Screw Zinc Phillips or Pozidriv, Pointed
CPP Flat-head Screw Chrome Phillips or Pozidriv, Pointed
RMN Raised, Countersunk Plain Phillips or Pozidriv
RMZ Raised, Countersunk Zinc Phillips or Pozidriv
RMP Raised, Countersunk Chrome Phillips or Pozidriv
RPN Raised, Countersunk Plain Phillips or Pozidriv, Pointed
RPZ Raised, Countersunk Zinc Phillips or Pozidriv, Pointed
RPP Raised, Countersunk Chrome Phillips or Pozidriv, Pointed
PJN Pan-head, Sheet Metal Plain Squared-off tip
PJZ Pan-head, Sheet Metal Zinc Squared-off tip
RJN Raised, Countersunk Plain Sheet-metal Screw
RJZ Raised, Countersunk Zinc Sheet-metal Screw
RJP Raised, Countersunk Chrome Sheet-metal Screw for trim panels
RWN Raised, Countersunk Plain Wood Screw
RWZ Raised, Countersunk Zinc Wood Screw
 


Codes for Washers

For washers the first letter indicates whether it is a plain or lock washer, the second letter, W, indicates it is a washer, and the third letter indicates the type of plating. The first digit following the letters indicates what type of washer it is, and the last two indicate the size of screw or bolt it fits.
TABLE A1-3 WASHER CODES
 
Letters Type Plating
PWN Standard Flat Washer Plain
PWZ Standard Flat Washer Zinc
LWN Spring (lock) Washer Plain
LWZ Spring (lock) Washer Zinc
 
First Digit
Flat Washers Specification
1 Standard washer, standard diameter
2 Standard washer large diameter
 
Spring (Lock) Washers
1 Spring (lock) washer, heavy section
2 Medium weight spring (lock) washer
3 Spring (lock) washer, heavy section
4 Medium weight spring (lock) washer
5 Spring lock washer with heavy section
6 Internal star washer
7 External star washer
8 Internal star washer
9 External star washer
 
Codes 1, 2, 6, and 7 appear in the 100 and early BN4 parts lists, while 2, 3, 4, and 5 show up in the later six-cylinder parts lists.
 
Last two
digits		 Size
02 Number 6
03 Number 10
04 1/4 inch
05 5/16 inch
06 3/8 inch
07 7/16 inch
08 1/2-inch
 
For example, PWN 104 is a standard 1/4-inch flat washer, unfinished, while LWZ 305 is a heavy-gauge 5-16-inch spring/lock washer.
 


Codes for Nuts

Nuts use an alphanumeric code with the three letters indicating the general type of nut, the first number identifying the nut specifications and the last two digits the screw diameter:
TABLE A1-4 NUT CODES
 
Letters Type Plating
LNN Stiffnut or Nyloc Plain
LNZ Stiffnut or Nyloc Zinc
FNN non-lock-type nut Plain
FNZ non-lock-type nut Zinc
 
First Digit Specification
1 Normal thickness and strength
2 Lock nut (half thickness) and normal strength
3 Castle nut, extra thick, normal strength
4 Castle nut, normal strength
5 Normal thickness but high strength
6 Lock nut (half thickness) and high strength
7 Castle nut, extra thick, high strength
8 Castle nut, high strength
 
Last two
digits		 Screw diameter
04 1/4 inch
05 5/16 inch
06 3/8 inch
07 7/16 inch
08 1/2 inch
 
So a normal zinc plated 1/4-inch nut would be coded FNZ 104, while a high strength, unfinished, 1/4-inch Nyloc nut would be coded LNN 604.
 

© Gary Anderson and Roger Moment, Austin-Healey 100/100-6/3000 Restoration Guide (Osceola, WI, USA: MBI Publishing Company, 2000), pp 183-186. Used by permission.
REF2.1