This information comes from a post on the now defunct forum "British Blades" by Joe Sweeney from the US, who was an ardent collector of Clasp Knives and an authority on WW1 equipment.
The pattern of knife on issue at the beginning of the war dated back to 1905 with pattern 6353/1905, 2 August 1905. This pattern replaced two patterns then on inventory, 116a/1902 'knives, clasp with marline spike, buffalo handle' and 4563a/1902 'knives, clasp with marline spike, black horn handle'.
The manufacturing instructions issued for pattern 6353 in 1905 describe the 'Knife, Clasp with Tin Opener and Marline Spike' as such:
3. The blade and Tin Opener to be made of best cast steel, free from flaws, properly hardened and tempered, and to be as thin and as well ground as the Standard Pattern; the edge of the Blade to be wetted on an oilstone; to be 3 1/2 inches long from 'kick' point, to be 11/16 inch wide; the Bolster to be 1/2 inch long, to be solid, and made from the best iron; the 'Springs' to be made of best spring steel, properly hardened and tempered. The Marline Spike to be made of cast steel, properly hardened and tempered. Length of Marline Spike when shut to be within 1/8 inch shorter than Spring; and the point, when shut, to be fitted close on the spring to prevent catching in the pocket.
4. The Length of the Handle to be 4 7/8 inches; the Scales to be checkered black horn 4 3/8 inches long Bolster 1/2 inch; to be riveted to plates with two iron rivets; the Shackle to be made of copper wire, No. 11 gauge, same size and shape as that of the Standard Pattern, and riveted with brass wire. The Blade, Tin Opener, and Marline Spike to be firmly riveted in, and to bear makers name on tangs.
The above specification description was modified in 1913 by the addition of specific dimensions for the tin opener to be 1 5/8 inches long by 11/16 wide. (this is in Flooks book the rest is not)
Very early in the war alternate patterns of knives were adopted to meet demands. Patterns were approved that introduced the clasp knife with only a tin opener and no marline spike. These patterns were 8171/1914 with Stag horn handle, 8172/1914 with checker black horn handle, and 8173/1914 with bone handle. All of these alternate patterns were declared obsolete on 18 May 1920.
The year 1917 saw a further introduction of a multitude of provisional patterns for clasp knives. Pattern 9401/1917, 26 April 1917, introduced 'Knives, Clasp with Tin Opener and Marline Spike with Nickle Scales'. Pattern 9402/1917, 23 April 1917, introduced 'Knives, Clasp with Tin Opener and Marline Spike with Fibre Scales'. Pattern 9403/1917, 20 April 1917, introduced 'Knives, Clasp with Tin Opener and Fibre Scales'. Pattern 9404/1917, 26 April 1917, introduced 'Knives, Clasp with Tin Opener and Steel Scales'. Dimensionally all of these knives adhered to pattern 6353, although material substitution was allowed, i.e. copper wire replaced by steel.
Patterns 9402/1917 and 9403/1917 were modified by patterns 9799/1917 and 9798/1917, respectively, on 12 February 1918. This modification simply specified that the tin opener should be ground bright and sharpened. Patterns 9401/1917 and Pattern 9404/1917 were not modified until patterns 9814/1918 and 9813/1918, respectively, were approved on 10 April 1918. This modification again simply specified that the tin opener should be ground bright and sharpened.
By mid war it was intended that only knives with Marline Spikes went to mounted men and those without Dismounted.