LEGO 8720 Motor Set 9v Set Parts Inventory and Instructions - LEGO Reference Guide
Lego 9V Technic Motors compared characteristics
BrickLink - Part 71427c01 : LEGO Electric, Motor 9V Mini-Motor, Heavier Weight [Electric, Motor] - BrickLink Reference Catalog
LEGO Technic 9 V 9 Volt Motor – Strong Pressure – Lego technique power motor in Light Grey – Can Be Used With The Current Motors, Cables: Amazon.de: Toys