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                                                                       EXHIBIT 6
                               GRADALL LETTERHEAD
 
                                                                    May 18, 1999
 
Dear Stockholder:
 
     I am pleased to inform you that on May 10, 1999, the Company entered into
an agreement and plan of merger (the "Merger Agreement") providing for the
acquisition of the Company by JLG Industries, Inc. ("JLG"). Pursuant to the
Merger Agreement, JLG, through a wholly owned subsidiary, has commenced a tender
offer (the "Offer") for all outstanding shares of the Company's common stock at
the offer price of $20.00 cash per share. The Merger Agreement provides that,
subject to satisfaction of certain conditions, the tender offer is to be
followed by a merger (the "Merger") in which the holders of any remaining
Company shares (other than dissenting shares) will receive the right to receive
cash in an amount of $20.00. The tender offer is currently scheduled to expire
at 12:00 midnight, New York City Time, on June 15, 1999.
 
THE BOARD OF DIRECTORS OF THE COMPANY HAS BY UNANIMOUS VOTE DETERMINED THAT THE
MERGER AGREEMENT AND THE TRANSACTIONS CONTEMPLATED THEREBY, INCLUDING EACH OF
THE OFFER AND THE MERGER, ARE FAIR TO AND IN THE BEST INTERESTS OF THE
STOCKHOLDERS OF GRADALL INDUSTRIES, INC. AND RECOMMENDS THAT HOLDERS OF SHARES
ACCEPT THE OFFER AND TENDER THEIR SHARES TO JLG.
 
     In determining to approve the Merger Agreement and the transaction
contemplated thereby, your Board of Directors gave careful consideration to a
number of factors described in the attached Schedule 14D-9 that has been filed
with the Securities Exchange Commission. Among other things, your Board of
Directors considered the opinions of Merrill Lynch, Pierce, Fenner & Smith
Incorporated, dated May 10, 1999 (copy of which is included with the Schedule
14D-9), to the effect that, as of such date, and based upon and subject to the
various considerations set forth in such opinion, the consideration to be
received, pursuant to the Offer and the Merger, taken together, was fair from a
financial point of view to such holders.
 
     The attached Schedule 14D-9 describes the Board's decision and contains
other important information relating to such decision. We urge you to read it
carefully.
 
     In a separate arrangement, MLGA Fund II, L.P., one of the Company's
principal stockholders, and certain of the Company's officers and directors (the
"Stockholders") have agreed with JLG to tender their shares into the tender
offer and otherwise support the transaction with JLG. MLGA Fund II, L.P., and
the Stockholders own approximately 34.4% of the outstanding common stock of the
Company.
 
     Accompanying this letter and the Schedule 14D-9 is the Offer to Purchase
and related materials, including a Letter of Transmittal to be used for
tendering your shares. These documents describe the terms and conditions of the
tender offer and provide instructions regarding how to tender your shares. We
urge you to read the enclosed material carefully.
 
     The Board of Directors and management of the Company thank you for your
loyalty and support over the years.
                                          Very truly yours,
                                          Barry L. Phillips Signature
 
                                          Barry L. Phillips,
                                          President and Chief Executive Officer