Original engine water temperature gauge sending unit for the early production M38, M37 and M42.  This original AC sending unit with Douglas connectors is for the early type gauges with the angled resistor on the back.  The later gauges used a different sender that is not compatible.  See the page out of the 1950 edition of the M38 parts book, SNL G-740 where this sender is listed.  Also see the picture of the gauge in question.  NOS sender in the sealed AC packaging.