It depends on who you talk to. Properly, there is a difference, but to many people there is not. I'd suggest that you ask if they really mean (mono)methyl siloxane and not dimethyl siloxane.

That is understandable but the suppliers are listing only dimethyl siloxane and i could not find listing for methyl siloxane. The application is to use as a lubricant.Any comments on using dimethyl in stead of mono methyl

Dear Salim,

poly monomethyl siloxane is a highly cross-linked solid (or colloidal particle) whereas poly dimethyl siloxane is the lubricant. The chain length will define the properties (the product data sheet may help).