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Short interest during the two-week period ending April 28 rose on two of four 3D printing stocks we follow. As of that date, all four stocks had posted year-to-date gains ranging from around 12% to 68%.

Short interest in 3D Systems Corp. (NYSE: DDD) rose by 3.1% to 25.69 million shares. Some 23.6% of the company’s float was short. Days to cover slipped from 16 to 15. In the two-week short interest period, the share price rose by about 8.1%. The stock’s 52-week trading range is $11.59 to $19.21, and shares closed at $19.07 on Tuesday, up about 0.3% on the day. Shares have gained 43.5% since the beginning of the year, and the 52-week high was posted Tuesday.

Stratasys Ltd. (NASDAQ: SSYS) saw short interest rise by 0.6% in the final two weeks of April to about 5.31 million shares, or 10.7% of the company’s float. Days to cover dropped from 12 to five. The share price rose by nearly 18% in the short interest period, and the stock closed at $27.86 on Tuesday, up about 2.4% on the day. The 52-week range is $16.37 to $28.00 and the stock posted its 52-week high on Tuesday. Shares are up 68.4% year to date.

Short interest in The ExOne Co. (NASDAQ: XONE) fell by 4.5% to 2.33 million shares. About 21.7% of the company’s shares were short. ExOne’s share price rose by about 6.1% in the two-week period. The stock’s 52-week range is $9.03 to $16.15, and shares closed at $10.51 on Tuesday, down about 2.8% for the day. Days to cover fell from 18 to 16 between the settlement dates. The share price is up 12.5% for the year to date.

Short interest in Voxeljet A.G. (NYSE: VJET) decreased by 0.7% to 512,290 American depositary shares, with days to cover remaining unchanged at seven. The share price rose by 16.8% in the two-week period to April 28. The stock closed at $3.62 on Tuesday, unchanged for the day, in a 52-week range of $2.61 to $5.62. It is up about 26% for the year to date.