Kelim, Chapter Fifteen, Mishnah Five
The general rule expressed in section three summarizes this halakhah well. A shovel is susceptible to impurity if it is used to hold things, even temporarily. This is enough to fill the requirement that the vessel have a receptacle.
However, if the shovel is used only to move things around, then it is clean because it is not considered to have a receptacle.
The rest of the mishnah is straightforward, so there is no commentary below.
1) The grist-dealers shovel is susceptible to impurity but the one used in grain stores is clean.
2) The one used in wine- presses is susceptible to impurity but that used in threshing- floors is clean.
3) This is the general rule: [a shovel] that is intended to hold anything is susceptible to impurity but one intended only to heap stuff together is clean.