X0204 3 2012-02-23 0 0001443669 Proto Labs Inc PRLB 0001542779 NBGE Manager, LLC C/O NORTH BRIDGE GROWTH EQUITY 950 WINTER STREET, SUITE 4600 WALTHAM MA 02454 1 0 1 0 0001218581 ANDERSON EDWARD T C/O NORTH BRIDGE GROWTH EQUITY 950 WINTER STREET, SUITE 4600 WALTHAM MA 02454 0 0 1 0 0001206641 DAMORE RICHARD A C/O NORTH BRIDGE GROWTH EQUITY 950 WINTER STREET, SUITE 4600 WALTHAM MA 02454 0 0 1 0 0001542781 NBGE GP, LLC C/O NORTH BRIDGE GROWTH EQUITY 950 WINTER STREET, SUITE 4600 WALTHAM MA 02454 0 0 1 0 0001542785 North Bridge Growth Management, L.P. C/O NORTH BRIDGE GROWTH EQUITY 950 WINTER STREET, SUITE 4600 WALTHAM MA 02454 0 0 1 0 0001390657 NORTH BRIDGE GROWTH EQUITY I LP C/O NORTH BRIDGE GROWTH EQUITY 950 WINTER STREET, SUITE 4600 WALTHAM MA 02454 0 0 1 0 0001197537 KINGSLEY DOUGLAS A C/O NORTH BRIDGE GROWTH EQUITY 950 WINTER STREET, SUITE 4600 WALTHAM MA 02454 1 0 0 0 Series A Preferred Stock Common Stock 5991790 I By North Bridge Growth Equity I, L.P. Each of the 427,985 shares of Series A Preferred Stock is convertible at any time at the option of the holder, and will automatically convert into shares of the Issuer's Common Stock on a 14-for-1 basis in connection with the closing of the Issuer's initial public offering. The number of shares of Common Stock reported on this Form 3 reflects the conversion of all shares of Series A Preferred Stock into shares of Common Stock on a 14-for-1 basis. The security does not have an expiration date. Represents shares held directly by North Bridge Growth Equity I, L.P. NBGE Manager, LLC ("NBGE") is the managing manager of NBGE GP, LLC, which is the sole general partner of North Bridge Growth Management, L.P., which is the sole general partner of North Bridge Growth Equity I, L.P. NBGE has sole vesting and dispostive power over such shares. Douglas Kingsley, a director of the Issuer, is a founding managing director of NBGE GP, LLC. Shared voting and investment power over such shares is vested in the managers of NBGE, Edward Anderson and Richard D'Amore. Mr. Kingsley, Mr. Anderson and Mr. D'Amore each disclaim any beneficial ownership of such shares, except to the extent of any pecuniary interest therein. This report shall not be deemed an admission that any of the reporting persons is the beneficial owner of such securities for purposes of Section 16 or for any other purpose. /s/ Catherine M. Verschelden, Attorney-in-Fact for NBGE Manager, LLC 2012-02-23 /s/ Catherine M. Verschelden, Attorney-in-Fact for Edward Anderson 2012-02-23 /s/ Catherine M. Verschelden, Attorney-in-Fact for Richard D'Amore 2012-02-23 /s/ Catherine M. Verschelden, Attorney-in-Fact for NBGE GP, LLC 2012-02-23 /s/ Catherine M. Verschelden, Attorney-in-Fact for North Bridge Growth Management, L.P. 2012-02-23 /s/ Catherine M. Verschelden, Attorney-in-Fact for North Bridge Growth Equity I, L.P. 2012-02-23 /s/ Catherine M. Verschelden, Attorney-in-Fact for Douglas Kingsley 2012-02-23