I have only been able to find one pattern of Clasp Knife marked Tatham. It is a first pattern. I would be very happy to hear from anyone who has any information as to whether any other patterns of Clasp Knife, or indeed any other models of knives were produced under the Tatham brand.
This knife is slightly heavier than the other first pattern clasp knives. The only significant difference with this knife is that it has a steel shackle, not a copper or brass one.