From Longman Dictionary of Contemporary Englishstock item/sizestock item/sizesomething that is available in a shop and does not have to be ordered → stock
Examples from the Corpus
stock item/size• Twenty five percent off stock items and 15 percent off ordered furniture.• He then needs to estimate the desired shelf stock size for each category on the basis of this record of use.• So we need to look for books that become standard stock items in schools.• Where this is impracticable, groups or categories of stock items which are similar will need to be taken together. 