Most of my multitool and knife holsters are designed for vertical carry. I described in a different thread how using horizontal carry at the 10:30 position is more comfortable for me when carrying heavier multitools:
http://forum.multitool.org/index.php/topic,56411.0.html.
An inexpensive, plastic Spyderco G Clip lets me convert most of my vertical belt holsters to horizontal carry on a 1.5 inch wide belt. You can purchase the Spyderco G Clip for about $10 from a web dealer.
The G Clip is designed to fasten to kydex type holsters so it comes with two Chicago screws and hardware. I don't use the screws, just the plastic clip itself.
The photo below shows a G Clip installed through the belt loop of a Victorinox SwissTool holster. The installation is not permanent and G Clip can be removed at any time.