The pieces offered here according to the model 500 parts catalog are 
# 1208 - Trip Tube and Plate Assembly.
# 20441 - Trip Rod Collar and Set Screw Assembly.
# 31078 - Manual Trip Rod
The manual trip rod varies in length from model to model - the rod offered here is about 3.75 to 4 inches long.

I know the Simplex models 312, 412, 616 and 716 use a rod this length.
Later models beginng with the 500 and continuing to the  1100 also require the # 25881 - Trip Rod Sleeve Assembly (I do not have any at this time).
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I think that the 4 inch trip rod is correct for models 1015, 1080, 1080A and 1100 if the # 25881 Sleeve is also used.
I think it is good for models 700 and 750 and might be OK for Model 24 and 600 also.
I know model 500 and 500-A use a 4.75 inch long rod, and I am guessing that the larger models 800, 850 and 950 use one longer than 4 inches also.