Selling different sizes in one lot of three

[ownerofit1946]

I have multiple sizes of a clothing item and would like customers to be able to purchase by lots 3 pieces in each lot in various or same sizes.

[shipscript]

If "three" is the magic number, then you will have to create the lots of "three". You will not be able to create a variation listing where individual items can be combined to make a lot of "three". 

You could entice a buyer to purchase three items by offering multi-purchase discounts, but it will not enforce a 3-item purchase.

If we look at this listing where the lot is three of the same item, then you could create a variation listing that offers different sizes, but each lot of three would be the same size.

https://www.ebay.com/itm/386132599095

A regular listing can not be converted to a variation listing. Instead, a new listing must be started as a variation listing.

Although the screenshots are older, this tutorial may help you understand variation listings:

https://shipscript.com/ebayhelp/lister_hub/creating_ebay_variations.htm