Sierra 18-5610 brand new starter opened only for pics. Fits Mercury outboards. Here is a description from another supplier 

Item: 5392

Description: Starter Motor 8 Tooth ARCO

  Mercury 100-125hp L4 87 & up

UPC Number: 693006001036

Weight: 7.6000

Cross Ref #: 18-5610, 50-66015 3

Mfg Part #: 50-66015 1,893892T

Price: