TheStreet.com Ratings provides exclusive stock, ETF and mutual fund ratings and commentary based on award-winning, proprietary tools. Its "safety first" approach to investing aims to reduce risk while seeking total return performance.

BOSTON (

TheStreet

) -- TheStreet.com's stock-rating model upgraded automaker

TST Recommends

Ford

(F) - Get Report

to "hold."

The numbers

: Ford swung to a second-quarter profit of $2.3 billion, or 69 cents, from a loss of $8.7 billion, or $3.89, a year earlier as revenue dropped 34% to $27 billion. Its gross margin rose from 6% to 18% and its operating margin climbed into positive territory. While Ford has $33 billion of cash, it has $133 billion of debt and $1.7 billion of quarterly interest expenses.

The stock

: Ford shares have tripled this year as investors reward the company for avoiding bankruptcy. The stock's high 2.5 beta means it's very volatile.

The model upgraded oil and gas producer

Concho Resources

(CXO) - Get Report

to "hold."

The numbers

: Concho lost $33 million, or 39 cents a share, in the second quarter after losing $14 million, or 19 cents, in the year-earlier period. Revenue declined 7% to $127 million. Its operating margin plummeted from 61% to 23% and its net margin fell deeper into negative territory. Just $3 million of cash reserves and a quick ratio of 0.6 demonstrate weak liquidity. However, a debt-to-equity ratio of 0.5 indicates restrained leverage.

The stock

: Concho has advanced 49% this year, outpacing major U.S. indices. The stock trades at a cheap price-to-earnings ratio of 13, but the company doesn't pay dividends.

The model upgraded investment manager

Northern Trust

(NTRS) - Get Report

to "buy."

The numbers

: Second-quarter net income surged 46% to $314 million, but earnings per share fell 1% to 95 cents because of its higher share count. Revenue dropped 21% to $1.1 billion. Its operating margin rose from 44% to 49% and its net margin increased from 15% to 28%. A debt-to-equity ratio of 2 suggests excessive leverage, but Northern Trust has $23 billion of cash reserves compared with $12 billion of debt, indicating outstanding liquidity.

The stock

: Northern Trust has increased 15% this year, more than the

Dow Jones Industrial Average

and the

S&P 500 Index

. The stock trades at an expensive price-to-earnings ratio of 26 and offers a lackluster 1.9% dividend yield.

We initiated coverage of

GT Solar International

(SOLR)

, which makes equipment used to produce solar cells, with a "hold" rating.

The numbers

: Fiscal first-quarter net income grew 51% to $7.8 million and earnings per share increased 66% to 5 cents. Revenue climbed 26% to $72 million. Its operating margin rose from 14% to 22% and its net margin expanded from 9% to 11%. GT Solar has less-than-ideal liquidity, evident in its quick ratio of 0.4. But the company has no debt.

The stock

: GT Solar has advanced 76% this year, beating major U.S. indices. The stock trades at a price-to-earnings ratio of 8, a vast discount to the market and peers, but the company doesn't pay dividends.

The model upgraded medical-equipment maker

Stryker

(SYK) - Get Report

to "buy."

The numbers

: Second-quarter net income fell 5% to $291 million, but earnings per share were unchanged at 73 cents, helped by a lower share count. Revenue dropped 5% to $1.6 billion. Its operating margin increased from 23% to 24% and its net margin was 18%. Stryker has an ideal financial position with minimal debt and ample liquidity, demonstrated by a quick ratio of 3.3.

The stock

: Stryker has advanced 4% this year, less than major U.S. indices. The stock trades at an attractive price-to-earnings ratio of 15, but offers a weak 1% dividend yield.

-- Reported by Jake Lynch in Boston

.

Follow TheStreet.com on

Twitter

and become a fan on

Facebook.