EXHIBIT A

Pursuant to Rule 13d-1(k) of Regulation 13D-G of the General Rules and Regulations of the Securities and Exchange Commission under the Securities Exchange Act of 1934, as amended, the undersigned agrees that the statement to which this Exhibit is attached is filed on behalf of each of them in the capacities set forth below.

Dated: February 26, 2019	SOTER CAPITAL, LLC
	By:	/s/ Mary Ann Sigler
		Name: Mary Ann Sigler Title: President and Treasurer
	SOTER CAPITAL HOLDINGS, LLC
	By:	/s/ Mary Ann Sigler
		Name: Mary Ann Sigler Title: President and Treasurer
	PE SOTER HOLDINGS, LLC
	By:	/s/ Mary Ann Sigler
		Name: Mary Ann Sigler Title: President and Treasurer
	PLATINUM EQUITY CAPITAL SOTER PARTNERS, L.P.
	By:	Platinum Equity Partners III, LLC, its general partner
	By:	Platinum Equity Investment Holdings III, LLC, its senior managing member
	By:	/s/ Mary Ann Sigler
		Name: Mary Ann Sigler Title: Vice President and Treasurer
	PLATINUM EQUITY PARTNERS III, LLC
	By:	Platinum Equity Investment Holdings III, LLC, its senior managing member
	By:	/s/ Mary Ann Sigler
		Name: Mary Ann Sigler Title: Vice President and Treasurer
	PLATINUM EQUITY INVESTMENT HOLDINGS III, LLC
	By:	/s/ Mary Ann Sigler
		Name: Mary Ann Sigler Title: Vice President and Treasurer
	PLATINUM EQUITY, LLC
	By:	/s/ Mary Ann Sigler
		Name: Mary Ann Sigler Title: Executive Vice President, Chief Financial Officer and Treasurer
	Tom Gores
	/s/ Mary Ann Sigler
	Mary Ann Sigler
	Attorney-in-Fact