** not tested , check the forum link below to check if it's tested by the time you read this ** The mark2 was tested with the olsson block in the 2th head, but for users that want to use there old UM2 head with the original fixed heater block, the 2th head is not low enough. Here's 2 options. Print the spacer to add 5 mm, or just print the head, it's 5 mm lower vs the base Mark2 head. Want to know more of this great option to add dual extrusion to the Ultimaker2? Main project info here; https://magnetic-tool-changer.com/ Questions? ask here; https://ultimaker.com/en/community/48788-ultimaker-mark2-the-smart-dual-extrusion-upgrade