Third-quarter sales were a record $1.44 billion, up 28% over the same period in 2020, and above our expectations.
Organic sales growth was 17%, acquisitions added 11 points, and foreign currency was a modest benefit in the quarter.
Overall orders in the third quarter were $1.55 billion, an increase of 37% over the prior-year period.
While organic orders were up an impressive 30% in the quarter.
We ended the quarter with a record backlog of $2.62 billion, which is up over $800 million from the start of the year.
Third quarter operating income was a record $338 million, a 25% increase over the third quarter of 2020, and operating margins were 23.4%.
Excluding the dilutive impact of acquisitions, core operating margins were 24.7%, up 70 basis points versus the third quarter of 2020.
EBITDA in the third quarter was a record $415 million, up 25% over the prior year, with EBITDA margins of 28.8%.
This outstanding performance led to record earnings of $1.26 per diluted share.
Up 25% over the third quarter of 2020, and above our guidance range of $1.16 to $1.18.
We continue to generate strong levels of cash flow, with third-quarter operating cash flow of $307 million, and free cash flow conversion of 109% of net income.
Sales for AIG were a record $982 million, up 31% over last year's third quarter.
Organic sales were up 15%, acquisitions added 16%, and foreign currency was a modest headwind.
AIG's third-quarter operating income was a record $245 million, up 20% versus the same quarter last year, and operating margins were 25%.
Excluding acquisitions, AIG's core margins were excellent at 27.2% in line with prior year margins.
Third-quarter sales increased 21% versus the prior year to $459 million.
Organic sales were up 20%, and currency added one point to growth.
EMG's operating income in the quarter was a record $115 million, up a robust 36% compared to the prior-year period.
EMG's operating margins expanded an exceptional 270 basis points to a record 25%.
AMETEK has had an excellent year with a record level of capital deployment, leading to the acquisition of 5 highly strategic businesses.
AMETEK is supported, approximately $1.85 billion on acquisitions, thus far this year, reflecting the strength of AMETEK's acquisition strategy and our ability to identify and acquire highly strategic companies.
In the third quarter, we invested over $75 million in RD&E.
And for all of 2021, we now expect to invest approximately $300 million or approximately 5.5% of sales.
For the full year, we now expect overall sales to be up in the low 20% range, versus our previous guide up approximately 20%.
Organic sales are now expected to be up low-double digits on a percentage basis over 2020, as compared to our previous guides of approximately 10%.
Diluted earnings per share for 2021 are now expected to be in the range of $4.76 to $4.78, an increase of approximately 21% over 2020 is comparable basis, and above our prior guide of $4.62 to $4.86 per diluted share.
For the fourth quarter, we anticipate that overall sales will be up in the low 20% range versus last year's fourth quarter.
Fourth-quarter earnings per diluted share are expected to be between $1.28 to $1.30 of 19% to 20% over last year's fourth quarter.
Third-quarter general and administrative expenses were $22.1 million dollars, up $4.8 million from the prior year, largely due to higher compensation expenses.
As a percentage of total sales, G&A was 1.5% for the quarter, unchanged from the prior year.
For 2021, general and administrative expenses are expected to be up approximately $18 million, driven by higher compensation costs were approximately 1.5% of sales, also unchanged from the prior year.
Third-quarter other income and expense was better by approximately $4 million versus last year's third quarter, driven by a $6 million or approximately $0.02 per share gain on the sale of a small product line in the quarter.
This gain on the sale was more than offset by a higher effective tax rate in the quarter of 19.5%, up from 17.5% in the same quarter last year.
For 2021, we now expect our effective tax rate to be between 19.5% and 20%, actual quarterly tax rates can differ dramatically, either positively or negatively from this full-year estimated rate.
Working capital in the quarter was 14.9% of sales, down 210 basis points from the 17%, reported in the third quarter of 2020, reflecting the excellent work of our businesses, and managing working capital.
Capital expenditures in the third quarter were $26 million, and we continue to expect capital expenditures to be approximately $120 million for the full year.
Depreciation and amortization expense in the third quarter was $75 million, for all of 2021 we expect depreciation and amortization to be approximately $295 million including after-tax, acquisition-related intangible amortization of approximately $138 million or $0.60 per diluted share.
In the third quarter, operating cash flow was $307 million, and free cash flow was $281 million.
With free cash flow conversion, 109% of net income.
Total debt at quarter-end was $2.65 billion, up less than $250 million from the end of 2020, despite having deployed approximately $1.85 billion on acquisitions, thus far in 2021.
Offsetting this debt with cash and cash equivalents of $359 million?
In the quarter-end, our gross debt to EBITDA ratio was 1.6 times, and our net debt to EBITDA ratio was 1.4 times.
We continue to have excellent financial capacity and flexibility with approximately $2.25 billion of cash and existing credit facilities to support our growth initiatives.
To summarize our businesses drove outstanding results in the third quarter, and throughout the first 9 months of 2021.

Summary:
Third-quarter sales were a record $1.44 billion, up 28% over the same period in 2020, and above our expectations.
This outstanding performance led to record earnings of $1.26 per diluted share.
AIG's third-quarter operating income was a record $245 million, up 20% versus the same quarter last year, and operating margins were 25%.
Organic sales were up 20%, and currency added one point to growth.
For the full year, we now expect overall sales to be up in the low 20% range, versus our previous guide up approximately 20%.
Diluted earnings per share for 2021 are now expected to be in the range of $4.76 to $4.78, an increase of approximately 21% over 2020 is comparable basis, and above our prior guide of $4.62 to $4.86 per diluted share.
For the fourth quarter, we anticipate that overall sales will be up in the low 20% range versus last year's fourth quarter.
Fourth-quarter earnings per diluted share are expected to be between $1.28 to $1.30 of 19% to 20% over last year's fourth quarter.
For 2021, we now expect our effective tax rate to be between 19.5% and 20%, actual quarterly tax rates can differ dramatically, either positively or negatively from this full-year estimated rate.