There are 5 sizes of RAM. The smallest is "A" and it goes thru "E"

The "A" size is for small items weighing less that 2 lbs.
The "B" size is one of our most popular size and your can mount anything that weights less than 5 lbs
The "C" size is our other most popular sizes, It does not carry any letter in the center of the part number it is recommended for 10 lbs.
The "D" size is our heavy duty size. It will hold up to 15 lbs.
The "E" size is our extreme heavy duty and will care up to 20 lbs.

The letter denote the center letter in the part number, IE: RAM-"B"-101 This is a B size. The RAM-101U is a "C" size, This is the only one of the part numbers that do not use the center letter.

All "B" size products work together, For example RAM-B-201U and RAM-B-238U and RAM-B-202U would all work together.

The "U" at the end of the part number simply denotes that the product comes in a Non Retail Packaging. All of our products are Non Retail unless otherwise asked for.