The Manfrotto 120-38 Tripod Spacer for Tripod Columns is intended for use with the 3263 Deluxe Geared Head. This spacer raises the head up from the tripod or camera stand, thereby allowing the camera platform on the head to reach fully its 90° tilt range. With 3/8" camera screw on top, and a 3/8" threaded socket on the bottom.
This spacer was exactly what I needed to gain the needed space between the head and the tripod.
So, it is well known that the bottom of the Manfrotto 323 RC2 System Quick Release Clamp is not flat because of the lever mechanism, which interferes with mounting on, say, a flat Arca Swiss plate. In addition, the part of the lever mechanism that contacts the plate must rotate freely in order for the lever to work properly. I installed the Manfrotto 120-38 Spacer between an Arca plate and the Manfrotto clamp intending that the lever mechanism would overhang the spacer and clear the plate. I didn't realize until after I installed the spacer that its diameter is too wide (61 mm) to clear the lever mechanism. In my picture, you'll see that I solved this problem by adding two stainless steel flat washers (3/8, 1.5 OD). I also added two neoprene washers (3/8, 1.5 OD) top and bottom to counteract spin.