Improper Thread Form : A general term describing an excessive deviation from a normal thread profile (in an axial plane) over a length of one pitch or over multiple pitch lengths. (Bul 5T1)
The Mudblogger (Oilfield, Energy and Related Photographs), Oil Field Glossary, TX, USA 2014. http://mudblogger.com/oilfield-glossary/, (Oil - Amer) {777}