'How to build a two valve set', No 3, Godfrey Philips cigarette card, 1925.
© Science Museum / Science & Society Picture Library
The reverse of the card reads: 'Screwing panel to Baseboard. The baseboard is of 1/2 inch softoft wood and measures 14 in x 7 1/2 in. the panel is fixed to the baseboard with two 1 in No 6 bras or iron countersunk screws, the necesary holes in the panel being countersunk with a rose drill. The screw holes are drilled with a 5/32 in drill 1/2 of an inch from the the edge of the panel and 2 1/2 in to 3 in from each end. The panel is then secured as shown; the operation will be greatly facilitated if the panel is supported on a pile of books or boxes whilst the screws are being inserted.'