What is the difference in a trailer brake acuator for disc brakes and one for drum brakes?

How do you tell which it is for. We purchased a used one and don't know whether to get disc brakes or drum brakes with it. Thanks.What is the difference in a trailer brake acuator for disc brakes and one for drum brakes?I think you will find they are drum. there has not been any improvement in trailer brakes. they have been the same for the last 70 years . any change would be a improvement.What is the difference in a trailer brake acuator for disc brakes and one for drum brakes?If these are air brakes the drum type has a long push rod which you cut to length then fit a yolk (usually 9 inches) the disc type have a sorter push rod that is not threaded and fits into the back of the calliper