Hi
Joe,
Thankyou very much for that research mate, I have done the same and think I have found Stevesandra's problem.
The 415H is a slightly heavier duty chain than the standard Scotty drive chain and consequently, the plate thickness is thicker.
This would not allow a standard joining link to be used, because the spring retaining clip would not be able to engage in its corresponding groove correctly, and would spring off in use.

The solution would to be IMO, to purchase a suitable joining link especially for the 415H roller chain.
Here are some specs for your info:
# 35 3/8 pitch x 3/16 width
410 1/2 pitch x 1/8 width
410H 1/2 pitch x 1/8 width
# 43 1/2 pitch x 1/8 width
415H 1/2 pitch x 3/16 width
# 41 1/2 pitch x 1/4 width
# 40 1/2 pitch x 5/16 width
# 50 5/8 pitch x 3/8 width
The following is the American National Standards Institute (eg.)ANSI Standard Chain Dimensions:
Chain No.
Pitch Roller Diameter Roller WidthSprocket thickness Working Load25 1/4" 0.130" 1/8"
0.110" 140 lbs
35 3/8" 0.200" 3/16" 0.168" 480 lbs
40 1/2" 5/16" 5/16" 0.284" 810 lbs
41 1/2" 0.306" 1/4" 0.227" 500 lbs
50 5/8" 0.400" 3/8" 0.343" 1400 lbs
60 3/4" 15/32" 1/2" 0.459" 1950 lbs
80 1" 5/8" 5/8" 0.575" 3300 lbs
Thanks again Joe,