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Short interest during the two-week period ending October 14 fell on half of the four 3D printing stocks we follow. Buying interest in the 3D printing stocks lifted share prices for all the players during the two-week short interest period. But short sellers don’t see that situation as sustainable for two of the companies.

Short interest in 3D Systems Corp. (NYSE: DDD) fell by about 3.1% to 24.67 million shares. Some 23.3% of the company’s float is short. Days to cover fell from 10 to eight. In the two-week short interest period, the share price fell by more than 19%. The stock’s 52-week range is $6.00 to $19.76, and shares closed at $13.91 on Tuesday, down about 1.4% on the day.

Stratasys Ltd. (NASDAQ: SSYS) saw short interest rise by 5% in the first two weeks of October to about 6.26 million shares, or 12.9% of the company’s float. Days to cover rose from six to eight. The share price fell more than 13% in the two-week period, and the stock closed at $19.75 on Tuesday, down about 1.6% on the day, in a 52-week range of $14.48 to $30.46.

Short interest in The ExOne Co. (NASDAQ: XONE) rose by 15.1% to 2.16 million shares. About 22.9% of the company’s shares were short. ExOne’s share price fell by more than 12% in the two-week period. The stock’s 52-week range is $6.50 to $16.15, and shares closed at $12.08 on Tuesday, down about 2.7% for the day. Days to cover slipped from 13 to 11.

Short interest in Voxeljet A.G. (NYSE: VJET) increased by 2.9% to 595,996 American depositary shares, with days to cover rising from six to 10. The share price fell by about 6% in the settlement period. The stock closed at $4.40 on Tuesday, down about 0.9% for the day, in a 52-week range of $3.50 to $6.99.