Overview Reviews Product Description The Mityvac deep well test adapter is designed for compression testing gasoline engines with deep spark plug wells. The adapter extends 8 in. beyond the installation surface and services both 14 mm and 18 mm threads. Mityvac Catalog Product Videos Custom Field Product Reviews Write a Review Write a Review × Mityvac Deep Well Test Adapter MVA5511 Rating * Select Rating 1 star (worst) 2 stars 3 stars (average) 4 stars 5 stars (best) Name Review Subject * Comments *