*

The remainder of this cover page shall be filled out for a reporting person's initial filing on this form with respect to the subject class of securities, and for any subsequent amendment containing information which would alter the disclosures provided in a prior cover page.

CUSIP No. 866942 10 5

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(1)

Names of reporting persons

Beverly L. Koski

(2)

Check the appropriate box if a member of a group (see instructions)

(a)  ☐        (b)  ☐

(3)

SEC use only

(4)

Citizenship or place of organization

U.S.

Number of

(5)

Sole voting power

339,111

shares

beneficially

owned by

(6)

Shared voting power

1,640,493

each

reporting

person

(7)

Sole dispositive power

339,111

with:

(8)

Shared dispositive power

1,640,493

(9)

Aggregate amount beneficially owned by each reporting person

1,979,604

(10)

Check if the aggregate amount in Row (9) excludes certain shares (see instructions)

☐

(11)

Percent of class represented by amount in Row (9)

6.2%

(12)

Type of reporting person (see instructions)

IN

CUSIP No. 866942 10 5

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(1)

Names of reporting persons

Christine L. Koski

(2)

Check the appropriate box if a member of a group (see instructions)

(a)  ☐        (b)  ☐

(3)

SEC use only

(4)

Citizenship or place of organization

U.S.

Number of

(5)

Sole voting power

125,752

shares

beneficially

owned by

(6)

Shared voting power

1,640,493

each

reporting

person

(7)

Sole dispositive power

125,752

with:

(8)

Shared dispositive power

1,640,493

(9)

Aggregate amount beneficially owned by each reporting person

1,766,245

(10)

Check if the aggregate amount in Row (9) excludes certain shares (see instructions)

☐

(11)

Percent of class represented by amount in Row (9)

5.5%

(12)

Type of reporting person (see instructions)

IN

CUSIP No. 866942 10 5

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(1)

Names of reporting persons

Robert C. Koski

(2)

Check the appropriate box if a member of a group (see instructions)

(a)  ☐        (b)  ☐

(3)

SEC use only

(4)

Citizenship or place of organization

U.S.

Number of

(5)

Sole voting power

60,000

shares

beneficially

owned by

(6)

Shared voting power

1,640,493

each

reporting

person

(7)

Sole dispositive power

60,000

with:

(8)

Shared dispositive power

1,640,493

(9)

Aggregate amount beneficially owned by each reporting person

1,700,493

(10)

Check if the aggregate amount in Row (9) excludes certain shares (see instructions)

☐

(11)

Percent of class represented by amount in Row (9)

5.3%

(12)

Type of reporting person (see instructions)

IN

CUSIP No. 866942 10 5

Page 5 of 10

(1)

Names of reporting persons

Thomas L. Koski

(2)

Check the appropriate box if a member of a group (see instructions)

(a)  ☐        (b)  ☐

(3)

SEC use only

(4)

Citizenship or place of organization

U.S.

Number of

(5)

Sole voting power

572,719

shares

beneficially

owned by

(6)

Shared voting power

1,640,493

each

reporting

person

(7)

Sole dispositive power

572,719

with:

(8)

Shared dispositive power

1,640,493

(9)

Aggregate amount beneficially owned by each reporting person

2,213,212

(10)

Check if the aggregate amount in Row (9) excludes certain shares (see instructions)

☐

(11)

Percent of class represented by amount in Row (9)

6.9%

(12)

Type of reporting person (see instructions)

IN

CUSIP No. 866942 10 5

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(1)

Names of reporting persons

Koski Family Limited Partnership

(2)

Check the appropriate box if a member of a group (see instructions)

(a)  ☐        (b)  ☐

(3)

SEC use only

(4)

Citizenship or place of organization

U.S.

Number of

(5)

Sole voting power

0

shares

beneficially

owned by

(6)

Shared voting power

1,640,493

each

reporting

person

(7)

Sole dispositive power

0

with:

(8)

Shared dispositive power

1,640,493

(9)

Aggregate amount beneficially owned by each reporting person

1,640,493

(10)

Check if the aggregate amount in Row (9) excludes certain shares (see instructions)

☐

(11)

Percent of class represented by amount in Row (9)

5.1%

(12)

Type of reporting person (see instructions)

PN

CUSIP No. 866942 10 5

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Item 1(a).

Name of Issuer:

Item 1(b).

Address of Issuer’s Principal Executive Offices:

Item 2(a).

Name of Person Filing:

Item 2(b).

Address of Principal Business Office or, if none, Residence:

Item 2(c).

Citizenship:

Item 2(d).

Title of Class of Securities:

Item 2(e).

CUSIP Number:

Item 3.

If this statement is filed pursuant to Rules 13d-1(b), or 13d-2(b) or (c), check whether the person filing is a:

(a)

[    ]

Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o).

(b)

[    ]

Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c).

(c)

[    ]

Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c).

(d)

[    ]

Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C 80a-8).

(e)

[    ]

An investment adviser in accordance with §240.13d-1(b)(1)(ii)(E);

CUSIP No. 866942 10 5

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(f)

[    ]

An employee benefit plan or endowment fund in accordance with §240.13d-1(b)(1)(ii)(F);

(g)

[    ]

A parent holding company or control person in accordance with §240.13d-1(b)(1)(ii)(G);

(h)

[    ]

A savings association as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);

(i)

[    ]

A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);

(j)

[    ]

A non-U.S. institution in accordance with §240.13d-1(b)(1)(ii)(J);

(k)

[    ]

Group, in accordance with §240.13d-1(b)(1)(ii)(K). If filing as a non-U.S. institution in accordance with §240.13d-1(b)(1)(ii)(J), please specify the type of institution:____

Item 4.

Ownership:

(a)

Amount Beneficially Owned:

(b)

Percent of Class:

(c)

Number of shares as to which such person has:

(i)

sole power to vote or to direct the vote:

(ii)

shared power to vote or to direct the vote:

(iii)

sole power to dispose or to direct the disposition of:

(iv)

shared power to dispose or to direct the disposition of:

Item 5.

Ownership of Five Percent or Less of a Class:

Item 6.

Ownership of More than Five Percent on Behalf of Another Person:

Item 7:

Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person:

Item 8:

Identification and Classification of Members of the Group:

Item 9:

Notice of Dissolution of Group:

Item 10:

Certifications:

CUSIP No. 866942 10 5

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February 13, 2019

/s/ Beverly L. Koski

BEVERLY L. KOSKI

/s/ Christine L. Koski

CHRISTINE L. KOSKI

/s/ Robert C. Koski

ROBERT C. KOSKI

/s/ Thomas L. Koski

THOMAS L. KOSKI

KOSKI FAMILY LIMITED PARTNERSHIP

By:

/s/ Christine L. Koski

Christine L. Koski, Managing Partner

CUSIP No. 866942 10 5

Page 10 of 10

/s/ Beverly L. Koski

BEVERLY L. KOSKI

/s/ Christine L. Koski

CHRISTINE L. KOSKI

/s/ Robert C. Koski

ROBERT C. KOSKI

/s/ Thomas L. Koski

THOMAS L. KOSKI

KOSKI FAMILY LIMITED PARTNERSHIP

By:

/s/ Christine L. Koski

Christine L. Koski, Managing Partner