We have at least one member with hands-on experience, but I'll try and explain shortly :thumbup:
Wake up at the back of the class Mr Meako, and pay attention! Tackler's knives have been discussed here many times!
In the days of the old textile mills, Tacklers were like Fitters in factories. They kept the looms and all the other machinery running. Clearing a blockage, be it yarn or a weaver's shirt-sleeve, had to be done quickly and efficiently, so they were supplied with knives. Many feature the names of mills or textile companies on the blade. A straight-edged knife was probably the most efficient design, and Tackler's knives usually have what is known, in the US, as a Wharncliffe blade. However, some are shaped more like a rounded Sheepsfoot :thumbup:
This example was made by Wheatley Brothers of Sheffield, who made a lot of Tackler's knives. The background is an interior photo of Salt's Mill in Saltaire, once the largest fabric mill in Europe. The building still stands today, and I have posted exterior photos of it here before (and recently). I seem to recall Mr Meako contributing to one discussion about self-effacing mill-owner Sir Titus Salt in relation to Tackler's knives
Hope this is helpful. An Ettrick knife is something quite different, and they are discussed at length in the Ettrick thread :thumbup: