This Spacer is sometimes needed to correct the fitment with Porsche and VW Engines.
If you are unsure measure your distributor and compare what goes into the block with the drawing here. If it measures 57mm to the bottom of the drive dog, (see illustration: 43+14) you will probably need the spacer.
Measurements = ID 27mm X 7mm tall
Most come with the spacer included and will say w/spacer.