Last week, the world's first 3-D printing mutual fund launched under the ticker symbol TDPIX. While the 3D Printing and Technology Fund may seem like a convenient way to get diversified exposure to the 3-D printing industry at large, there are far too many unknowns with the fund at this time to determine if it's a sensible investment vehicle.

Among other things, investors in the fund are essentially flying blind until the fund releases its quarterly holdings, which it isn't expected to do until sometime around the end of March or early April. Although investors can get a sense of the investment criteria from the prospectus and deduce that 3D Systems (NYSE:DDD) and General Electric (NYSE:GE) are likely holdings, there's far too much risk in not knowing the specific allocations.

In the following video, 3-D printing analyst Steve Heller sits down with the head of The Motley Fool's industrials bureaus, Blake Bos, to discuss why investors should avoid this fund until its holdings are released. (The relevant video segment can be found between 18:44 and 21:38.)