Philips sets using metric screws?

[Silicon]

When I discovered that a machine screw was missing in my Philips 170A/15 domestic radio (1946) I assumed it was a B.A. size.

It has a slotted cheese head and screws directly into the bakelite case.

However a 5mm (0.8mm thread) screw fits nicely. The original screws/bolts are 4.85mm in diameter.

I had assumed that the radio was made in Mitcham and therefore would use imperial screws.

What can you tell me about the fixings used in Philips and Mullard wireless sets?

[paulsherwin]

I haven't noticed this, but it doesn't surprise me. They all use 4mm banana plugs rather than Wander plugs.

[emeritus]

If it screws directly into the Bakelite case (i.e. there is no threaded metal insert), then it might be a 10-32 self tapping screw. The tables in my copy of Machinery's screw thread book gives the max diameter for No 10, 32 TPI, self tappers as 0.1890", which is about 4.8mm, and the pitch of 1/32" is pretty close to 0.8mm. Perhaps the specified tolerance on diameter was relaxed in the late 1940's: worn machine tools could have had to be used for screw production beyond their design life, given the continuing shortages of everything in the austerity of immediately post-war Britain (so I am told). Slight oversize would be less of a problem in a self-tapping screw. 10-32 was one of the preferred sizes for Unified screws in the UK.

[Maarten]

Too see where your Philips product was made, have a look at the letter in front of the serial number. If it's an M, your set was made in Mitcham, but could still be designed or partially designed elsewhere.

['LIVEWIRE?']

Relative to the above, where would a Philips 'Superinductance' 274A have been made, and when? I reckon in 1934 or thereabouts in Britain, but the seriakl no. has no prefix letter. There is a Makers no. stamped inside the cabinet, which has '34' as the last 2 digits, and on the cabinet back a label stating 'designed for use with British Valves marked with the letters 'B.V.A', but can anyone confirm my suppostions?

[Maarten]

Before approximately 1935 it was a bit more difficult to determine where a Philips set was made. I suspect you may be right, but I don't have any firm information on that.

[Silicon]

I checked a few more screw threads in the 170A.
I have a vernier caliper and a thread guage.
The 4mm screws are 3.9mm in diameter and the treads are 0.7mm.
The 3mm screws are 2.9mm in diameter and the treads are 0.5mm.

The 3mm screws were a tight fit in a new 3mm nut.

The serial number starts with an M. It seems that the chassis screws are all metric.

[julie_m]

I would have expected a Continental-based manufacturer to use Continental fasteners throughout.

There probably would be no import tariff, for want of any UK manufacturer making metric fasteners at the time; the earliest relevant British standard I can find is BS3643:1967.

[emeritus]

According to the 1969 edition of Machinery's Guide to World Screw Threads, the BSI issued a War Emergency Standard Specification covering the SI Metric screw thread in 1943 as B.S. 1095: 1943. The book says that that standard was subsequently withdrawn as it "no longer represents the standard metric threads used in the UK", but gives no date for its withdrawal or the identity of the BS standard that replaced it.

It transpires that France, Germany, and Switzerland all had their own metric screw standards. While there was considerable concordance in diameter/pitch combinations for 6mm diameter and above, the French 3mm thread had a pitch of 0.6mm. M3 x 0.5mm corresponds with the German DIN (and ISO/SI )standard. The national standards differed in the dimensions of the truncation and presence/absence of rounding at the crests and roots of the screw and nut profiles.