Q: My partner holds certain professional equipment, which he claims is his, whereas I claim that it belongs to the business. What is the halachah?
A: Neither partner can claim something known to have belonged to the partnership without proof that he subsequently acquired sole ownership of it, even if he holds it for a long time. This is because partners are not particular about allowing each other to hold joint property. According to some authorities, if he held the equipment for an excessively long time, more than typically tolerated, he is believed when he claims that it is his; others do not differentiate (C.M., Sma and Taz 179:1; Shach and Gra 179:2).
However, if the disputed property is not known to be in a partner’s hands, so that he could deny holding it, he is believed to say that he holds it, but that it is his (migo). Similarly, if it is unclear that this equipment initially belonged to the partnership, one partner can claim that it is his private property (Pischei Choshen, Shutfim 7:30, citing Mabit 2:73).