The inclusion of a second wheel to the pivot and as importantly the removal of the stop is an ingenious way to counter for wear. Any slackness is taken up by the claws ability to continuously press against the wheels on the pin through the contraction of the springs.
Robert Adams, Smith & Turner, James Adams, William Tonks and others all have models that incorporate this lay out and method of achieving a draft free, safe and secure building.
As always feel free to comment readers and thanks to Paul and Diane for their hospitality and desire to get the 2860 Smiths working correctly.