Container holder for adapting smaller diameter container

An assembly for delivery of a medical substance comprising:

• a housing suitable for use with one of a plurality of containers containing a medical substance, wherein the plurality of containers have different outer diameters;
• and
• a container holder for receipt within the housing and comprising a shoulder at a proximal end of the container holder,
• wherein the housing comprises one or more internal projections at a distal end of the housing for blocking distal movement of a first container when the first container is received within the housing, wherein the first container has a first external diameter, and
• wherein the housing further defines one or more inwardly projecting ridges provided proximally from said one or more internal projections, wherein the one or more ridges are configured to abut the shoulder to block distal movement of the container holder, which holds a second container, when the container holder is received within the housing, wherein the second container has a second external diameter which is smaller than the first external diameter, and wherein the second container, when received within the container holder, extends distally from the shoulder.