Never saw them on manual transmissions, probably because the trans is a seperate piece from the bellhousing and the bellhousing itself doesn't need any bracing. On an auto trans they are all one piece and it puts more stress on the bellhousing to have all the weight hanging from the bellhousing which is aluminum instead of cast iron. I know that some of the later manual bellhousings are also aluminum, but they also have more webbing to bolster their structure than the cast iron units. Just a guess of course, but I'm stickin' with it!!!LOL!! Geof